Replacement knobs (GForce and GMajor)

Hello - from years of gigging (and incessant tossing about by drunk/disgruntled/underpaid roadies) I am missing 1 of each of the following:

G Force     parameter/value wheel

Gmajor    adjust (inner) wheel

I've been getting by by "swapping" knobs back and forth, from shaft to shaft, but it's aggravating...can anyone point me towards where I might be able to get replacements for these?  I can't imagine it's be a huge problem, right?