You might check the book on Moravian Gun Smiths, unfortunately, I do not have it.
Looking through RCA, in the Christian's Spring section, the only one with a brass patch box is #43, which is unadorned and fairly plain. It has no side plates, and a rounded nose on it, more oblong than you would see on a wooden patchbox.
All the others either have a wooden patch box, except one that has a brass side opening box that Shumway says is a modern replacement.
Wish I had more references for you.
Cheers,
Norm