If you want some really nice fish, its best to import them from Thailand, which should be doable. But if you can't, there are some nice breeders in the US.
I find that most American bred fish don't have the same finnage quality.. But I'd say if you wanted to buy within the US, look up
Martinismommy (she goes by that name on Aquabid and on forums, and has a few auctions going on AB
right now, so look her up!).
Hopdiggity on Aquabid sells Thai imports on Aquabid and has a few auctions happening right now for pretty cheap.. she doesn't sell pairs and none of the fish she's selling right now would make a good pair. She also has a website called LuvMyBetta.com and is known as LuvMyBetta on forums.
Basement Bettas is another great breeder and I like the finnage on her fish. That link goes straight to her sale page. She has a few fish up for sale and a Pair of Copper Halfmoons that are proven breeders, so take a look.
84elmo2001 is also an American seller on Aquabid... their fish seem pretty ok, but you need to be picky as not all of them look that great.