Honestly this is why I suggested you email them versus cold calling. Even still, they may choose to ignore your email, but if they reply...you then have a copy of the communications. All of this can serve as supporting documentation for the police.
If you are set on calling around versus emailing them, I also suggest looking up local regulations for pawnshops in your area, if you are going to call and they give you the run around you can cite the appropriate regulations/legal requirements they are subjected to follow. Key holder or not, they are obligated to know these regulations... taking in/trafficking in stolen merchandise is bad business, and it happens a lot. Granted there are shops that are shady and do it anyway, but generally speaking it is not in their best interest to trade in stolen merchandise and those regulations are there to help protect the shop's liability and assist the potential victim and assist the police in recovering merchandise.