An excellent resource is Mental Prodigies
(Greenwood Press, New York, 1952), by English magician Fred Barlow. It contains biographies of many of the classic lightning calculators (including the only woman among them). In the book there is also a section on magic. You will find several gems there. My favorite is “Magic Addition”, a piece that Larry Becker popularized under the name of “Some Total”. Harry Lorayne included his very practical take on it in Mathematical Wizardry
. The best version I know, however, is the brainchild of Los Angeles mentalist Greg Arce. So clever that you will want to try it right away.
Barlow devoted his life to magic, and died when he was 101. His obituary:http://www.times-series.co.uk/news/596752.0/
If you have trouble finding the book, just request it at your local library. LAPL and NYPL both have copies of this wonderful book.