The best place to get them is at a reptile show if you are looking for frozen ones. You can usually get rat pups for about $.80-$1.00each.....much cheaper than a pet store. There is a show coming up next weekend in Oaks, PA....about 30-45 min from South Jersey.
I have never been to Oaks only the Hamburg show and yes they have live pups there for <$1 never priced frozen.