I bought my first 1.2 pair from Petco, and had no idea that I needed to wait for the females to get to a certain age before breeding. Took about 6 weeks for me to get my first litter, but it was healthy (11 babies), as have all others been since then. I'd say they're (mice) a little difficult to get started breeding, but once they do they won't stop.

My advice is the same as has already been given here. Find a local store that sells feeder mice since they probably breed their own. They'll be able to get you started with a 1.2 group of appropriate size/age.

As for me, I'm getting my first 1.2 rat group this weekend hopefully...