I am not sure this is the correct category to post my question. What the pictures depict is a lever that takes a slip-on knob. This is a 1963 Webcor Squire tape recorder I'm working on. There are 2 identical knobs, and one is broken. My problem is that I don't know what these are called or where to start looking for new knobs. They don't have to look like this. In fact I'd rather they were metal, at least the one that is broken, as the original was under-designed for the amount of force needed to put the machine into record. The one that you see in the photo is fine. The shaft it goes on is the "edit" lever, which requires hardly any force at all. Does somebody know how to go about finding such knobs? Thank you.

Not many radios used flat-shank controls. They seem to have been peculiar to high-torque applications such as tape decks. You might have better luck looking in a site that specializes in tape recorders... Facebook may have a group that can help.

Thank you. You might be right, although I've seen these sorts of knobs on all kinds of things. As for FB, not hardly.

You might do best to cast some replacements out of aluminum, but then you run into the issue of having a metal surface that could become electrically live.

You might try the Voice of Music guys. I haven't dealt with them personally, but it might be worth emailing.
https://www.thevoiceofmusic.com/other_recorder_parts.html

A fairly straight forward project for someone with a 3-D printer. Maybe there's a college where it could be done by students?
Could be carved from wood or plastic. I have some off-cuts from recycled plastic planks that could be shaped with files and sandpaper.