Aquabid is a good resource but most will end up costing you a LOT, because of the international shipping.
I've been out of bettas a long time too, but I used to be in contact with the "local" betta club too. www.ibcbettas.org can get you in touch with quality betta breeders.
Honestly, having seen and bred really high quality bettas, I don't ever see a decent betta in petsmart, petco or any of those box stores. I rarely see anything worth it in even fish stores.
If you want real quality, check out the IBC and find a breeder. You'll be wowed by the fish you see there. Also, aquabid is awesome for window shopping, even if you don't buy because of the internation shipping, there are a few US breeders on there, but you'll still pay shipping to get the fish.