Look on Craigslist for people selling their fancy rats. A lot of the time you will find Russian Blues, Siamese, Dumbos, etc. Most only ask a few dollars for females, even super nice ones.

From there, hold back traits you like, cull the others. The only thing that is a guaranteed cull for me is mother's that eat their young. I don't care if it's their first litter, it will certainly be their last. I produce an average of 14 babies per litter though. I didn't really hold back offspring of the females that produced well on purpose, but I ended up with high litter counts anyway.

In my opinion, even as a rat pet owner, Doggy Bag is fine for feeders. I have a friend with around 300 rats and he produces very large litters on Doggy Bag. His adults all appear pretty healthy as well.