(hope it's okay to post with ideas even if we don't work for the stores?)
Dry: I've gotten Coral Frenzy from Gabe's before. Many of the ingredients in it would be suitable for filter feeders.
Liquid: Aquarium Designs carries a lot of the Reed Products and there are quite a few that would be good for filter feeders.
Frozen and Live: Polly's Pets has a great selection of frozen including Oyster Eggs in frozen cubes and frozen Coral Food by H20 as well as DT's Phyto, etc.
Personally I wouldn't buy stuff like bottled and on the shelf forever Marine Snow, etc. but that's just me. I either go dry, refrigerated liquid or frozen to avoid as many fillers and additives as possible.
But even the same brand can have different versions or stuff. Like free dried cyclopeeze is just the little pods (perfect) but the wafer form includes fillers, etc. Got to read the info on the package and see what's acceptable to you and what isn't.
What are you trying to feed anyway? (there are differences to what different filter feeders will want to eat)