Well, there are "dwarf" BCI's like Central American boas, Sonoran desert boas, Hog Island boas, Cuban boas, etc. Are you looking SPECIFICALLY for Boa constrictors, or are you looking for a boa in general, like a Rosy boa or Kenyan Sand boa? Both of those don't get big at all, I think max is like 3-4 feet if that.

Jennifer