Try one of the auction houses!
Shotgun News and Gun List normally have advertisements from auction houses that specialize in firearms. maybe they can help.
My grandfather ran a pawn shop in the 1930s, and when he died, my grandmother had to sell everything he had in the store plus the collectables he kept for himself. Another gun dealer took them all, but he apologized to my grandmother, explaining that he couldn't give her full retail price for them because he's have to sell them again and make some sort of profit.
It seems to me that selling them as a lot to another dealer wouldn't give you their full value. Auctioning them as a group, or individually, could put more cash in your pocket.
Do well.
- - - Yoda