I don't think anyone actually sells them, as they are so simple to make. All sorts of things can be used from spare bits of vinyl, hoover tubes split down one side, or in my car a couple of old steering rack gaiters.
All you need is something flexible that will wrap around the rebound spring and can be held in place with a couple of zip ties.
For a permanent solution, fit hard chrome kingpins, available from all the usual sources. I got mine form John Worrall
