Hello Brian, I Do Not have an RCA knob for you but have a 3D printed knob for a Packard Bell 5N. This knob is just under 2″ across and the length of the shaft is just over 1″. It is designed to fit on a split shaft. It was made by a friend and gifted to me. You can see ripples in them from printing, can be sanded smooth.
I’m offering this if nothing better comes your way. Cheers.
John