well there is
DPFishways, (most of my fish are from here and are stunning!) the website is being worked on at the moment, but i know he still has loads of males in the shop so could be worth phoning and asking.
The Betta Lady, (my friend dusky has had a male and female from here and they are really lovely too)
SQBettas, (not seen any from here in person, but the photo's look good. although some of them seem quite pricey for what they are.)
K.G.Bettas (had a couple of girls from here, though they were clearance stock so i think they were slightly older than is common, but well priced. was not impressed with the way they were packed and sent personally, but thats just my opinion)
ebay is always worth checking too, can get some great bargains on there!