the 3 i go to are....
tropicana fish(tropicana and pecos): just picked up an 8 inch lapradei bichir from there for 30 bux!, also got 2 crenicichla xingu 1's
F.I.S.H.(charleston and bruce): a few years ago i picked up a baby payara arnatus, they have a good selection sometimes
Lucky Tropical Fish(spring mountain and decatur): always stocked with some rare fish. i picked up a snook cichlid for 14 bux they are selling at petsmart for 30. always got some cool ass flowerhorns and they have some monster fishes... big aros, big dats, i once saw a 2 foot baramundi there. if u talk to the owner he can probably order u anything u want. i think this is the best rare fish store in town.
those are the only 3 LFS here in vegas i go to.. i dont bother with the rest.