Have that knob for almost 20 years. It was a leftover from my amp building days and laid in my drawer for all that time. However, that kind of knob is not difficult to find. Just search 'volume knob' on eBay or AliExpress, look for one with 15mm outer diameter and 6mm D (half) type shaft. Knob with set screw can be used as well, but might need some adjustment. Original height is 9mm, so anything higher is fine. That one I used is 14mm, which sticks just a little more out than I like. I reckon 12mm will be just about perfect for me. Might order a few more to try as volume knob is generally pretty cheap.
Your great ideas were helpful. thank you