Very few people in the UK breeding them at present... they have always been something of a minority breed, they just don't have the glamour and cachet of their "Lassie" sisters. I haven't really looked into it to a great degree, but if we have so few breeders taking an interest in them here, then it's much less likely that anyone would want to bring some in from abroad. Then there is the issue that some overseas reg bodies allow rough x smooth breedings - our KC doesn't, so that might preclude a much needed injection of new blood. If they aren't already an endangered British breed then they soon will be.
I'm just a fan of Mastiff type dogs Btw I did a quick edit of the profile just before posting the link as I wasn't 100% happy with it, much better now