Sutlers generally don't market beyond the confines of their tent at events -- a sign listing what they have or what service they provide, and typically a scrawl about something on sale. Those online are about the same way. So let's call that captive marketing, vs active marketing, of which they do very little: they occasionally buy space in an event folder or sponsor a speaker or musical performance or something.
Bottom line it's all nitch marketing to a nitch audience. Mass marketing isn't justifiable given their minimal marketing budgets. Facebook page if they have time to keep it current. In my view of it most sutlers run on a pretty thin margin; a love of history and reenacting keeping some hanging in there when from a business standpoint they should have shut down long ago
In regards NPS or State Park historical site stores, they don't do much active marketing either, just signs in their stores. Hear's some advice though - have one of your local college art or marketing departments make up professional-looking artwork promoting your historical CDs. Have that art reproduced on thick stock (poster board) and perhaps have it laminated and a folding prop put on the back. It might not cost as much as you think, maybe $150. for 50 copies or so. This is known as a POP (point-of-purchase) display.
When you first talk to these history venue store managers you then offer to provide them your very attractive full-color POP display. It's an incentive. Common marketing strategy in the for-profit world, but not much utilized in the non-profit world (park stores, museum stores).
Admittedly I'm getting a little bit carried away for the scale you're probably thinking about ...but since you asked.
Wonderful CD btw. Mine arrived yesterday.