My experience would suggest that rats are easier and more effective than mice or gerbils. Regarding ASFs, Heath (TekWarren on here) has a great little ASF forum.

www.asfrats.info

There's an advertising section there for breeders with surplus litters. There is one girl shipping them, but she has some sketchy threads on the BOI and I would recommend that you read those and then decide for yourself if you buy from her. My understanding on these guys is that the main cost is shipping them...it runs around $80 or so. The result is that they are spreading more slowly by hand-to-hand transport and purchase, and so are taking a while to become available in some areas.