For girls, you can find them at Petsmart, Petco, Walmart, etc. They're listed as 2 bucks, usually.
Be careful to look for an ovipositer, so you don't buy a plakat male by mistake.
The number one rule about keeping females together is ATLEAST have 4.
Any more than four is always better, to level out aggression.
I suggest a 10 gallon, if you plan on having up to 5. Any more than that, I'd say get a 20 or 30 gallon. As always, bigger is better.
Breeding is another thing entirely, and explaining it in a nutshell would be impossible.
You should start another thread for that, probably.
But yes, just make sure you have atleast 4, and ready yourself for some bullying, as they have to establish heirarchy. Some people have noticed their females NEVER stop bullying, so be prepared for that as well.
If you're keeping them in a divided tank, with another boy, I'm curious about the size of the tank..
If you've got a 20 or 30 gallon divided so that the boy gets room, but the girls get the most of the room, then it would be okay.
Dividing say.. A 10 gallon between a boy and four girls would be bad bad bad.
And, the only place other than established pet stores would be local fish stores, and they're going to be the same quality, ish, of the petstore bettas.
If you want BREEDER girls, you'll need to order off of
Aquabid.com
Which is pretty expensive.
I suggest starting out with some pet store fish, before you move on up to expensive breeder females.