I saw this posting whilst I was searching for related material.
I don't know where to buy this stuff (sorry), but I thought I could add my two-cents to the post:
Many years ago, I had a German Shepherd Dog (actually two...) who developed "Hip Displasia" (if I spelled it correctly). This is a common hip disease for the breed. My dog would scream in pain during either sudden movement or even mild movement after a long period of rest; to the pont where I thought he was going to have to be destroyed. Usual traetments of the day (early 1990's, by the way) did not work - and I spared no expense trying either. My vet then learned of Cartrophen, and suggested that he try it on my dog. I agreed. It WORKED! As in 100% effective - it literally cured my dog of a supposedly incurable disease. I thus vouch for the product (well, in dogs anyway...).
Good luck trying to find it - perhaps a vet in the UK could help?