It's unfortunate so much time has passed, but I would guess that if you mention the letters ATF to any self respecting gun/pawn shop that they would be very willing to cooperate. We're dealing with a felony here!!! I don't think it would be unreasonable to offer to buy the gun back at a reasonable price instead of getting the ATF involved, especially since you already own it.

I have seen a gun, stolen from me, on gun show tables twice in a couple of decades. I have not felt comfortable grabbing it and running the first time, or explaining my situation the second time and trying to work something out. The fellow who displayed the gun the second time is a friend, now deceased, but explaining the situation and expecting a good result would be asking too much. If I see the gun again, I may have a different attitude.