By all means, if you can find out what the thread size is, you can use a knob that will fit.
Here is the part I found on the web:
page B.of the diagram, part number 47 of the diagram
Part number 286303-00 Clamp Knob Assembly $12.03
You may also be able to find this exact part number on e-bay or on the web at a cheaper price.
Good Luck and God Bless! Spirithorse