It is illegal to sell native fish without and commercial liscense. They are very pricey, that's why you do not see many people who sell natives. That's also why if you have natives that you want to get rid of, you have to give them away and cannot accept money.
LFS have native mostly as bycatch in shipments of feeder fish and ghost shrimp. They sell the natives quickly and whether they know what it is or not. They let them go for dirt cheap (usually as feeder price) to get rid of them no questions asked. I have gotten numbers of bluefins, seminole killies, swamp darters, etc in ghost shrimp tanks. If you get a chance, check out those tanks and you'll get some nice treasures!