I saw this website has two similar ball roasters (and in Spain!):https://www.machinio.com/cat/ball-roaster
I feel like I had seen at least one of those machines listed on another site, too, though I didn't find it in a quick Google search.
There are also these two Barths, though I'm sure they're more than you'd want to spend for museum display purposes:
Schokoma in Germany sometimes has old ball roasters, though there's nothing listed on their site now. You may ask them anyway, in case they just have something unlisted.
Finally, I have no transaction history with these websites - nor any history buying antique roasters. I just stumbled across these recently while researching, and thought I'd share. Good Luck - sounds like a fun project.