I'd love to find some kind of reference book that has pictures of this type of sheath or other equipment
This particular type sheath is in many ways an original creation of Karen Shook. While there are original rawhide and rawhide covered sheaths (usually done as a repair over an exiting sheath), there are in fact very few 18th century knife sheaths of any style in existence, and especially frontier styles are virtually non-existent, except for a fair number of Indian made and quilled sheaths. Karen may have some sources I don't know about which she has used to inspire her work.
There are quite number of existent 19th Century sheaths (which most of my work is inspired by), both of Indian and "white" manufacture so there is a pretty fair amount of research resources available for them.
Several books are available showing 19the Century sheaths, in particular John Baldwin's, Early Knives and Beaded Sheaths of the American Frontier.as well as websites such as
www.splendidheritage.com,
www.bbhc.org,
www.longrifle.ws, and several of the antique/old west auction sites such as
www.Cowanauctions.com and
www.aawt.com to browse.
As for this type sheath and the ones that I make which are not copied exactly from originals, I think of them as "Period Possible" - gear inspired by the materials, workmanship, and style/look of documented period gear, but which are not exact copies or which can't be documented.
What other type gear specifically are you interested in? I should be able to point out some other info for you........