We also corresponded via email, but for the sake of other readers, the Moog MG- slider knobs look very similar, but will not fit because the M500 switch lever is a different shape from the Moog slider lever.
I suggested a Juno-106 Portamento switch lever might work (though it is certainly a different look):
If you try this out, please let us know the results!
Thanks again Sam I didn’t try the Juno-106 switch knobs yet, but someone I know mentioned the Monotribe switch knobs. Do you think these Monotribe switch knobs could work?