Who to call:

“…make lots and lots of phone calls to animal control agencies to see if anything turns up. And, of course, if you have a known offender, start there. Rodent rescues, shelters, humane societies, SPCAs, all those kinds of organizations may have heard something also (or helped prosecute, depending on the jurisdiction).”

Questions to ask when you call:

“Are they aware of any ‘underground’ breeding operations?
Any ideas who runs it or how to contact them?
Where do the local herp stores get their feeders?
Ever had any problems with animal cruelty in the herp stores?
You can also call around to herp stores and ask the same question - anyone local run a breeder operation, who, where, etc.”

Also…

“keep an eye out for stories of large numbers of rats suddenly being dumped at shelters/rescues (or not :/ Even if
they are healthy, it can be an indication of a breeder getting rid of excess ’stock’”