Bully Library...
 
These are just a few books that I thought would offer some good information.  Some, such as the "The Bullmastiff, Peerless Protector" are no longer in print but can be found on e-bay and may be in libraries.    The book "Dog Eat Dog" is more of a just for a fun read book, it is about the show world, but it centers around bullmastiffs and mainly AllStar Bullmastiffs, it is entertaining.

Here are the books in no particular order:

Bullmastiffs - Mary Prescott...published in 1995 by T.F.H. Publications, Inc.
Pet Owners Guide to the Bullmastiff - Janet Gunn...published in 2000 by Ringpress Book(Interpet Publishing)
A Complete Pet Owner's Manual BULLMASTIFF - Dan Rice DVM...published 2006 Barron's Educational Series, Inc.
A Kennel Club Book Bullmastiff - Juliette Cunliffe...published in 2006 by Kennel Club Books, LLC
The Bullmastiff Manual "The World of Dogs"- Bill Walkey published in 1999 by Kingdom Books
Bullmastiffs Today - Lyn Pratt ...published in 1996 by Howell Book House
The Bullmastiff Peerless Protector - Jack Shastid and Geraldine M. Roach published in 1999 by Howeel Book House, A Simon and Schuster Macmillian Company
Dog Eat Dog - Jane and Michael Stern published in 1997 by Scribner

ASSOCIATIONS

The Bullmastiff Fanciers Of Canada - gives you information such as Rescue news, show and upcoming events, Canadian Breed Standard and a listing of Breeders in Canada that are members of the Fanciers.  The site is
http://www.bmfc.ca

The American Bullmastiff Associaion is http://bullmastiff.us