Those Siltronix rigs use a fairly commonly available knob at least. I'd be surprised if you couldn't buy boxes of them new if you needed to. I had a 1011C once upon a time. Sent it off for a problem that I didn't know how to repair at the time, and the guy working on it had one of the speed nuts that held the bottom in place fall and short something out. He couldn't fix it, so he sent it somewhere else. Then the shop closed and I had no idea where my radio got to. Never did get it back. That was part of my impetus to learn how to work on my own gear, so I guess it was a worthwhile lesson.