Thanks for the feedback and suggestions.
Sorry if I made it sound like I've never sold a gun before. I've bought and sold many, many, many -- gun stores, online sites of all kinds, gun shows and in person (though mostly modern pieces; relatively few antiques). I used to have an FFL in CA, in the days before the paperwork got to be too much of a headache.
The one sales forum I haven't had much experience with is auction houses. I'm surprised no one here knows of a good one. Maybe that says more about the state of things in the auction business than anything else....