A quick Internet search looks like Grant published a four-volume series. The original Single Shot Rifles has about 20 pages of Maynard info, much of it drawn from catalogs. More Single Shot Rifles has 11 pages of Maynard info, much of it discussing two special rifles and also a table of cartridge dimensions. I haven't seen the other two books in that series. If you don't have it already I would highly recommend George Layman's "A Guide to the Maynard Breechloader," which is packed with good info.