I don't know what area you are looking in, but I was looking at Old English Mastiff breeders and found one that also breeds Giant Maso Mastiffs: Thunderheart Farm English Mastiffs. http://www.massivedogz.com/default.asp? As with almost any breeder's site it isn't pretty, but I think their dogs are very good-looking. When I am ready for a dog I'm going to get a Maso from them!
You can purchase a Giant Maso through the website http://www.massivedogz.com/ . As of 9/21/2010 they have some females who will be ready to go the week of 11/2 - 11/9. They DO ship to other states and they do personal pick-ups if you live locally (the breeder is located in Virginia)
THERE IS A COUPLE IN LAKE ANN VIRGINIA THEY ARE THE ONES WHO STARTED THIS BREED AND THEY ALWAYS HAVE PUPS
Thunderheart farms in West Virginia.
1500 bucks liter i f 14 just born this week