Did a thread like this awhile back, and it was pretty successful.
I've got a stupid amount of underwear, /soc/, so throw out a request, and I'll match it the best I can!
Pick a color(s), stripes/dots/solids/etc, and cut (boyshort, thong, bikini, hipster, etc.) I'll see what I can do for you. :)

Also have a few swimsuit bottoms (and tops?) I might throw in if requested.