I don't think you'll find anyone breeding sables, but to make them yourself you need reds and black tans. In England sable is genetically a red tan (Ay/at). I could point you to a couple of people with nice reds, but I don't know any black tan breeders personally.
They are difficult to breed for showing because they are prone to a lot of faults, more than self or tan mice, and you need to keep a fairly big stud if you are showing them because you can guarantee 95% of them will have some kind of moult mark when show day comes. Also, because of the red gene, they are prone to being obese and won't breed, so they have a short show life and you need to breed them younger than most other varieties. If you're not worried about showing then they're no more difficult than anything else!
There's some information on breeding sable here:
http://hiiret.fi/eng/breeding/varieties/sable.html
Here's one I had, bred by Humbug Stud:
He was beautiful, I am very fond of sable.
Sarah xxx