I googled orthopaedic leg support for dog and there seems to be quite a few places ( mainly American ) that have lightweight canine leg braces. http://www.mypetsbrace.com/front-leg...paw-braces.php
I would agree that in the first instance it would be a good idea to go back and speak to Clare Rusbridge. She works with bionic vet Noel Fitzpatrick, so she may possibly be able to get a little advice about supports for you.
The buggies really work well for frail dogs.
I also hate SM. It is terrible to see your pet suffer. I do hope you told Tilly's breeder about her diagnosis. When there are top breeders still using young stud dogs that have been diagnosed with SM under the age of two, it sometimes seems that the only owners concerned about cavalier health issues are pet owners.
Cavaliers......Faith, The Ginger Tank and Woody.
Japanese Chins.... Dandy, Benny, Bridgette and Hana.
Remembered with love......... Tommy Tuppence and Fonzi