gunbroker is ONE possible venue- however- there are auctioneers that specialize in highly collectable firearms. This is ONE of those companies you might check with: http://www.armsbid.com/
You might also email Mr. Jim Supica, the curator of the National Firearms Museum in Fairfax (NRA HQ). Jim used to run Olde Town Station, which did much of that type of selling- and see if there is a company he could suggest to handle the sale. Please do NOT ask Jim to establish a value of your gun (value of an item is what it will bring at a sale- old axiom).
Or you could avoid all the hassle and make one moderator very happy by wrapping the gun securely, and ship it to me. I will love it, care for it, and shoot it now and again, and think nice things about you.