Have you tried, "The Prop Builder's, Mask Making Handbook" by Thurston James? I've used it for some of my mask making classes.
It's an excellent and inexpensive general mask making book with chapters on virtually ALL types of mask-making, including; papier mache, latex, mold making and numerous other materials and processes.
It's very well illustrated with photos and step by step instructions. I got mine at Amazon.com for under $20.
Other information about it: Published by Betterway Books, 1507 Dana Ave.,Cincinnati, Ohio 45207
ISBN 1-55870-167-2 (hardcover) ISBN 1-55870-166-4 (paperback)
GOOD LUCK