I got my original rat stock from a chain pet store, but I got my female mice from Craiglist and the male from a small time pet store. There is a rat fancier society, but I'm not sure if they sell their offspring for people to breed or not, so I'd just get ones from other people. I'm hoping to start another rat colony when I can make room, so CL will probably be my go-to place when I get to that point. Right now I've got the skeletons of 2-3 mouse colonies, just need to grab some more females.