Jim and Millie B. from Illinois wrote me a few days ago, asking if I knew of any reference books on antique fishing flies.
No, I don't, because there aren't any. At least not any good ones. Most of the pertinent reference material is spread through flyfishing books on more general historical topics.
One good one is Paul Schullery's "American Fly Fishing: A History," which seems to be out-of-print but with used copies selling on amazon.com for about $20. If you have a specific question about a particular fly, you might try contacting the folks at the American Museum of Fly Fishing. Andrew Herd's fly-fishing history website is also worth a look.