You could post a request for a rat breeder in your area under business forums here.

You could ask around about any local reptile shows in your area or within a reasonable driving distance.

You could put up a note at a local pet store (most provide a bulletin board for this sort of thing).

You could put a note up at a feed/tack/farmers supply type store on their bulletin board.

You could look for a privately owned pet store that may breed their own rodent stock in the back.