I have enquired about this for my rottweiler, apparently they are now available in Australia

OrthoPets: Orthotic Brace or Prosthetic Device for Dog or Animal, including Stifle, Hock, Carpus, Elbow, Knee, Wrist, Ankle, or Paw

They make movable braces for dogs with weak legs and mobility problems. I think anyone out there who wants a good brace to help larger breeds this is the way to go! My Rottie has a collapsing hind leg that bends inwards and finally there is something out there for him! Cost isnt too bad either for something custom made

Pets In Motion in Melbourne are doing them, if you are not in melbourne then you can have a cast made at your local vet and the product shipped out to you.

http://www.dogleggs.com/files/carpalbrace.cfm

these ones are also available at a lower price or smaller problems.