Is there a website? I’m interested ....
I'm sure there is a network of social media communication within their ranks. Eg.: forums, or FB or whatever. Maybe someone will come on here to chime in with an exact link for you.
I just know that .... several years back, I posted a pix of an 1890s small-west-coast town dog tag. Someone PM'd me and asked if I wanted to sell it. That led to a conversation with the fellow, who ... at the time, gave me various information on the rarity scales (Ie.: what fetches demand and prices, etc....).
From the conversation, I realized I should not immediately take his offer. So instead I told him
"I'll float it on Ebay, alert you to when it's listed, and secretly tell you my hidden reserve price". So that in that way, I'd be fair to myself, and it would be "open bid".
It ended up getting several bidders, including a name or two that I recognized that he'd told me were big time buyers (essentially "driving the market"). So that told me that .... while it was a niche collectors gig, yet .... you know the drill: Those in specific niche collector circles tend to get to know who each other are (and vie for the best collections, etc....).
I don't have any links for you, but either google will be your friend, or someone might come along with links.