I live in Brooklyn and I only visist stores in Brooklyn. The only three worthy stores are:
Brooklyn Aquarium Inc
339 9th St, Brooklyn, NY
(718) 499-1483
Brooklyn Aquarium Inc is dirty as hell but they always have awesome Cichlids, usually stuff you can not find anywhere else. Also you will come across a ray or an aro once in a while.
and
World Class Aquarium
2015 Flatbush Ave, Brooklyn, NY
(718) 258-0653
World Class Aquarium are a bit more pricey but they always have very healthy stock! Whenever I am there someone is always doing water changes, I do not think I have seen one dead fish in this store. They will have some awesome looking Discus, Angels, time to time rays, Frontosas, etc.. They got this what looks like 180+ monster tank with bunch of huge Cichlids, they got this one male Red Devil that is way over a foot long! Also they got an awesome policy in exchanging fish or if you are trying to trade in your fish for something else.
Fish Expo
2370 Nostrand Ave, Brooklyn, NY
(718) 253-6400
Owner was always an ass to me, ****ty policies as far as returning fish, or trading in fish (basically they never do it). But they have basically the best African Cichlids in whole Brooklyn. They had this young guy working there, cool guy always loves to yap about fish.
I think those are the only three stores I would buy serious fish from. The rest are Petlands (I think there are around 6 driving distance from me alone!) and other crap along those lines.