Rio's Kennels have some massive 100lb+ ones but insist they are all from Game stock. Rio's website has loads of info on it though. Loads of it about cos it's big money game in the states.

A staff isn't just a terrier, it's an old english bulldog crossed with an extinct type of white english terrier to create a more compact dog that could still do the damage as the terriers were baiting dogs too. They bred English Bull Terriers from the same stock but added dalmation for the white and bits of other things then when they got the head they wanted, massively inbred them which resulted in a lot of deaf dogs.