Bettas are very stressful to breed. When I was younger, like 11 or so, I stupidly tried breeding them in a 2 gallon bowl. The female jumped out in the middle of the night. They're not nice fish.
I have since read up a lot on it and I think 10 gallons is the mininum, not sure about the other fish in there. Do you have lots and lots of plants and hiding spots like pots and such? I was wondering if I could breed a male with my female with the guppies in the tank, although the male would probably attack them.
Yeah it's hard to find female bettas at all, atleast around here, and so it's especially hard to find younger or prettier ones. The local wal mart actually had a shipment in of young females, so you never know where you'll find them. I got one, I think the rest pretty much died in there. I hate wal mart. I wanted to buy them all and have a community tank.