Bell, R. C., The Building Medalets of Kempson and Skidmore, 1796-1797, Frank Graham, Newcastle-upon-Tyne, 1978, 183 pages, hardcover with dust jacket. This is an excellent book if you need something more focused than Dalton & Hamer. Mr. Bell talks about the history of each piece and rarity of any varieties known. If you are doing more than just building a collection this book is invaluable, ex James Farr Collection Library.
Estimate: 10-20 USD