You could do a good search for a breeder near you, or ask a few vets if they know of any. I JUST learned from my vet's front desk girl that she is getting rats soon from her friend who is a breeder about 1/2 a county away from me. I am definately gonna check that out next time I want a ratty. There is always Petfinder.com where you can search for rats needing homes, to be adopted near you.
I have adopted a few rats from petco before. They told me they were mismarks that came from a breeder because they normally only have p.e.w. rats. So far 2 out of 4 rats I got this way have been cancerous in their old age. One of them is neurotic beyond belief, afraid of her own shadow and I have not been able to change this as I have with other rats and rodents. Two lived to a good old age but passed away from little respiratory ailments which they didn't fight off too well because they were so old. One was a mismarked himilayan who became perfect marked when she got her final coat and a complete ball of rolly-poly love.
My fiance's family has free-adopted 3 rats from petco who were "dumped" there because their owners didn't want them or take good care of them. One was mediocre, a little jumpy and nippy. The other two turned out to be mean little things, not their fault since they were supposedly ignored and mistreated by the person who gave them up.. of course they seemed fine at the store.
Its a mix of good and bad.. basically I just don't trust everything they say at all anymore.
I am not fond of getting rats from those types of stores, I think I will stick with my local family owned pet shop where I have shopped all my life and had 3 of my best rats from, all who were snake feeders.
In the future I look forward to getting my rats from this breeder I heard of and maybe this new pet shop that breeds and sells rats for pets only, they handle them great and often have ones with powder blue color, hooded and self. So gorgeous.