The only place I can find females are at PetCo, the LFS doesn't sell them.
I havn't had Panda Corys, but at work we have a very aggresive Betta named George, we've had him for a year and a half, he's very big and loves his five gallon, but one weekend my boss thought he looked lonely and threw him two albino corys with him. I was shocked on Monday when I arrived and he hadn't killed them, but in fact he loves them and could really care less what they do in "his" tank. I was surprised.
I've never had trouble with a betta and corys, but then again the ones I've had were non-aggresive, whereas George is a very angry little man, lol. He constantly flares at me when I walk past the tank and even when I feed him.