Vegas is kinda bad for fresh water, i only have been able to find a couple of good lfs one is Trop-Aquarium, its a bit overpriced but good selection and you can order fish from them if they don't have the kind you are looking for.
another store is Atlantis on lake mead, store is small sometimes they have good fish, but i had bad exp with them, every time i go there i see dead fish in their tanks so i don't buy from them.
lucky fish is another good store i found, but they only carry large size fish and they don't order any fish from the supplier for you.
i been trying to find some tigers shrimps here but i haven't had any luck, all u find is stores here are red cherry. so let me know if you find any.