My local PetCo has some pretty nice Bettas usually, but the next town over at their PetCo, they have much MUCH higher quality Bettas. They sell HMPK's, Doubletail Halfmoons and so soo many others. The only thing is alot of their Bettas get sicker faster, I think it's in their water. Alot of their fish (not just Bettas) seem to have scoliosis and their Bettas after a few days of being there seem to get ammonia poisoning much quicker then my local store and even my local WalMart (which does NOT care for their Bettas at ALL).
But yeah, you can find some really beautiful fish at PetCo, even PetSmart and WalMart occasionally get some really really pretty Bettas in.