STEP 1 - Get some balls!
(Yeah, sorry...this post is going to be full of unfortunate phrasing/wording...rather than try in vain to avoid the dozens of inevitable double entendre, I'm just going to totally give in. You've been warned)
This is some of my stash of Christmas/Halloween vase filler from Michael's from last year's clearance sales (with a FDC garland at the top...more on that below). That may give you an idea of what kinds of colors you might be able to find, though seasonal items are always honestly a bit of a crap shoot:
I don't do much craft supply shopping online because I prefer to actually see and feel them in person. However, since these are tough to find even when they're "in season" and damn near impossible to find after Christmas, going online may be your best option. You'll also get a broader range of color and size options. Bear in mind that if you don't like the color you can change it (I'll post on that another day), but it's easier to buy a color you like in the first place. Here are some online options:
Factory Direct Craft
Factory Direct Craft has some pretty excellent options for glittered foam balls, specifically garlands and the somewhat unfortunately named "ball sprays."
The garlands are awesome because they're a good price and already have holes in them, but only come in two colors: platinum and red. The platinum is really pretty - the mix of silver and gold reminds me of vintage mercury glass.
The ball sprays come in more colors (including white which is a great base color if you're planning to layer an iridescent sheer/pastel glitter over it), but at 6 for $1, this is one of the pricier options included here.
I bought a few shades of Christmas Central decoration glitter balls via Walmart,com. These are pretty similar size (diameters range 0.8-1.25") and price-wise (about $6 for a bag of ~60) as the bags from Michael's. I found the quality a little uneven: the white ones had hardly any glitter on them, but were fine for layering over. Everything else I tried was beautiful and there are a lot of cool color options (I especially love the lake green, gunmetal silver and bright yellow shown here).
The Blushing Iris on Etsy
I had a good experience shopping with The Blushing Iris Etsy Shop. The bags include are a wider range of sizes than the other options I've listed (about 100 little ~0.5" balls and 100 larger ~0.8" balls).
Hobby Lobby (?)
I don't really shop at Hobby Lobby, but they do have glitter ball vase filler and "foam glitter ball confetti" on their website (for example, this Red, White and Blue mix here). Not sure if it's in stores and/or how long it'll be stocked (might be seasonal like Michael's)
The other thing you need is pipe cleaner. You can buy them in packs from craft stores, but I also like to use the garland spools from Factory Direct Craft because I don't have to twist two together to make a longer handle, I can just cut whatever length I need. I would get the metallic ones and try to generally match the color of the balls you're using so if a little peeks out of your handle it's camouflaged.
To string them on to purse handles, the ball will need punched through them to thread the pipe cleaner through. Balls that are strung on garland are ready to go (unless you want the hole bigger). If your balls are on wires (like floral picks), you'll need to pull those off first:
If your balls aren't garland (i.e. vase filler or picks removed from their wires), you make a hole through the middle with a tooth pick. The foam balls are soft, so it should be easy to poke through. Tip: if you're using ball that have been removed from wires, try to line the toothpick up with the spot where the wire was attached, otherwise you'll have a wee ball spot where there's no glitter.
Once you've got your balls prepared, there are two methods for attaching new handles to the purse. The first method is more structurally sound because you actually thread the pipe cleaner through the purse, while the second is a little easier. As usual, there's no "right way" - both methods have pros and cons, try both out and see what works for you (or invent something new that works even better!!)
Step 1. Punch holes in the purse where you'd like your handles to go. If it's like a bucket-shape purse sometimes you only need one hole, but on purses where it's a flap that comes over the top you may need two. I have a tool I inherited for putting wee holes in fabric for setting grommets (grommet pliers, that I would assume were purchased at Joann's) but you probably don't want to buy one just for this....you can also poke holes with little scissors or cut very small incisions with an Exacto knife.
Step 2. Thread the foam ball with the hole in it onto the pipe cleaner, all the way to the end covered the twisted together end. Covering the twisted ends will prevent any untwisting/unraveling and will cover the pipe cleaner.
Step 3. Keep threading on the foam balls in any pattern you like:
Step 4. If you reach the end of the pipe cleaner, but you'd like your purse handle to be longer, twist on another pipe cleaner. When you're close to the end of the first pipe cleaner, twist another one on there and then continue threading balls, pushing them over the spot where you've joined the two pipe cleaners. As with the first ball, covering the twisted join up prevents unraveling
Step 5. Once your purse handle reaches the desired length, it's time to attach the other side of the strap to the other side of the purse.
Feed the pipe cleaner into one hole and out the other, then pull it so the last ball in the handle is flush against the purse (don't pull it too tight yet because you're going to need a little wiggle room in a minute)
The other way to add a foam ball handle is a little easier, and if you have a purse that doesn't have a good spot for punching holes you can still use this approach.
Step 1. String balls onto a pipe cleaner in your desired pattern
Step 2. When the strap is the desired length, pull off the last ball on either end and trim the pipe cleaner ends so they're just long enough to reach almost all the way through those last balls (I do this by cutting the pipe cleaner just below the last balls, then pulling them off, then snipping off a teeny bit more)
Step 3. Add a little bit of hot glue inside the end balls and slide them back onto the ends of the pipe cleaner. The hot glue should get a really nice grip on the foam and the bristles of the pipe cleaner. Be careful - the hot glue might melt the foam a little, and I wouldn't want anyone to get burned!
Step 4. Hot glue the strap onto the purse. When the hot glue is dry, if there's a lot of it visible where you stuck the handles on, you can cover it with glue and glitter.
(1) A teeny little bit of marabou trim wrapped around the base of the purse handle looks really cute and can cover up the spots where the handle attached in case you aren't thrilled with how it came out.
(2) Foam balls also make great "feet" for purses that won't stand up on their own. I like to make sure a purse can stand up for display purposes, so I like to add either foam balls or glass stones for feet.
3. You can mix in other foam embellishments besides balls for cute effects. They need to be that same light kind-of styrofoam density so the strap doesn't sag, but keep an eye out for cute stuff to repurpose. I originally got these stars from Papermart.com, but they don't seem to be in stock right now. However, I know Michael's will have a ton of cool Christmas picks including some foam embellishments soon (if they don't already), so check that aisle out when it goes on clearance. I've seen wee little foam skulls for Halloween at Michael's and there are usually great little glittered foam eggs around Easter (won't help you this year, but if you work year-round like I do you'll be ready to grab them)
If you have questions/ideas, let me know if the comments!! Happy glittering!!
UPDATE 1/25/2017: I've noticed that if you use the second method (where you hot glue the strap onto the purse rather than threading the pipe cleaner through the actual purse on either side), the hot glue can lose it's hold. What's likely happening is that there's enough loose glitter that the whole shebang can peel off. If this happens, I would recommend using a nice generous dollop of E6000 between the purse and the hot glue blob. This is a pretty good strategy in general when you encounter hot glue appearing to "peel up" off one surface - the cooled hot glue blob will have conformed nicely to the surface to give you a good contact area and the E6000 is a little stronger but too runny to hold something big in place. I'll try to add some pictures of that process if I get a chance.