Not all of them are from abroad.
I can't say where all the distributors are for each of those retail chains, but I know my store (a PetSmart) has one of the better distributors amidst my company and our Bettas come from Utah. The distributor is a fishery and it appears as though they produce all of the fish that they sell.
I imagine each of these companies has a number of distributors that they use, and so to really know you may have to speak to someone at the stores to learn about what distributor they have. Not sure how the question might be taken, however -- that may depend on who you ask.
Something tells me though that international distributors are unlikely, or few, in the case of major chain stores. I could be wrong, however.