Hi,
I believe a patellar tendon strap is the kind you're referring to? Where I am, they are not that difficult to find in drug stores. I bought mine from the local grocery/pharmacy store. It's a Tensor brand strap with a neoprene sleeve around it.
I got one because I have patellar tendinosis. After the most recent recurrence, I could not even walk without a significant amount of pain. Since I've started wearing the strap, it's been easier to carry out the basic activities of everyday life, like walking at work, housekeeping, etc... the strap reduced the pain quite a bit. It may not be the cure for the problem, but it's been a help in pain management, for me.