I know what you are going through! I had a custom Colt 1911 stolen out of my uncle’s vehicle in WA years ago (yes I was a LEO at the time) and I still haven’t heard anything on it.

Do two things. 1). Make up a data sheet on the weapon with any pictures of a similar looking one. 2). Make contact with ALL the little nickel add centers, pawn shops, gun shops, LE Agencies in WA, OR, ID, and get them a copy with contact info A.S.A.P.
Offer a reward for the return of the weapon can hurt (Even if you do a “No Questions Asked”!) and may help get it off the streets before someone get hurt or kill. It takes some time to put it together, but it needs to be done.
Hope this helps and ya get it back soon!
ArticWolf