I got mine from Petco, since it was the perfect size for my nightstand.
The one I got was 3 gallons, but I bet PetSmart has different sizes.
But pick what you want ^___^
Aaaand for a heater, this is great
I can't find the one I have (it's a flat, circular heater with a suction cup that I anchor under the gravel) but this is basically the same thing...
HOWEVER, if you go to Petco and go to the betta section, I can almost guarantee you'll find mine. It's still in stock at my Petco and it's a popular item.
This one is for 2-10 gallons. It's great.... mine is for 1-5 gallons. Since mine is 3 gallons it's perfect.
PetSmart has the same general things (also my heater, but I couldn't find it on the PetSmart website either) so good luck with your fishy!!