I started of with rats from petsmart, petco and a local pet store selling reptiles (at the time I did not know anyone breeding rats so my choice was limited), took time to establish a strong healthy colony but it was worth it.

I never bought adults however, I have always bought small rats raising them up to breeding size simply because if you buy adults they might already too old too breed.

The best way to start a colony with good genes is to pickup a few animals from a local breeder.