I believe that's already an aftermarket style switch. I have a similar one with a knob that's held on with a setscrew. The original style has the knob permanently attached to the shaft, with a latch to release the shaft from the switch for installation or removal. I don't know of a source for a knob separately, but any knob you might find at a hardware store would work. Your picture looks like the switch is in the ON position. Will the shaft push in? Here's a clip from Jim Carter's web catalog.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
