If I suspected a local perpetrator in the burglary, I would post, prominently, a $5000 reward for return of the gun and information about the burglar. That may bring someone with information out of the woodwork. I suspect that a gun thief in a case that I am familiar with was "outed" by his wife who was dissatisfied with his lifestyle and having to share space at home with a bunch of stolen guns. It could work for your friend. Good luck.