Here are lists of books about Casio calculators from the Royal Library
of the Kingdom of Sweden:
http://libris.kb.se/hitlist?q=casio+fx&d=libris&m=10&p=1&s=r
http://libris.kb.se/hitlist?q=casio+cfx&d=libris&m=10&p=1&s=r
Two of them are in English:
Explore mathematics with Casio CFX-9850G, CFX-9950G / by Per Broman
ISBN 91-88064-09-3
Mathematics with graphing calculator : [extra textbook for Casio
CFX-9800G and fx-7700/9700GE] / [Per Broman]
ISBN 91-88064-08-5
I have one Swedish book about Casio fx-7700 (actually fx-7700GE) and
those above are probably translated and improved versions of that. I
think my book is rather worth reading for Casio-users. I'm normally a
Texas Instruments (TI) user and Casio is new to me.