BettaTalk.com
There are good crowntail bettas and there are many more inferior ones. If you plan on breeding, one of the best sources in the U.S. is BettaTalk.com. Faith is the online Betta expert at BettaTalk.com and breeds exceptional quality bettas including giants. They are pricier than most but they are the BEST and have an extensive pedigree (Faith has been breeding them for a while and knows all parents, grandparents, etc.)
If you just want a showy crowntail and do not plan to breed then Aquabid might be o.k. There are a lot of novice sellers on Aquabid however and a lot of U.S. fish are poor quality/pet store types. You'll notice the inferior bettas on Aquabid by the markings after you've seen the fish at BettaTalk.
We did purchase a black butterfly off Aquabid from a Thailand breeder, however we are convinced that the fish we received was NOT the same as the one pictured in the auction. It was quite stressed from shipping too. Overseas sellers will ship to someone in the U.S. who will in turn, ship to you. You will incur shipping charges in the overseas country as well as additional U.S. shipping charges, which are usually overnight or 2nd day charges.
You may also do a web engine search. If I recall, there is at least one big betta breeder in Florida.
Good luck!