Mark has or had a drivers backrest but I think he may have sold it. Here is the thread he had which details what it looks like and also has the dimensions so you could conceivably make it or have it made. http://www.vmaxforum.net/showthread.php?t=5417&highlight=backrest
I hope this helps, as I don't think there are any vendors that make these, at least there are none that make them anymore. Good luck in your search.