I looked through some old threads, and it seems like you could still get them direct from Elektron (at least up to 3 or 4 years ago) but I wasn’t sure if that’s still the case.
MD knobs & MnM knobs are the same.
MK1 units of both silver boxes (and early mk2 units maybe?) used hard plastic knobs while later models all use rubber coated knobs that look almost identical to the original plastic ones.
The OEM plastic knobs are really hard to come by these days sadly. If you are ok with the soft touch rubber knobs, contact Eleketron diretly for the best prices on replacements.
For non coated knobs, I did a short write up of various plastic/aluminum knobs I found online that will work for the units that look similar:
I really don’t like the rubber coated knobs but if they’re you’re thing the elektron replacements are you’re best bet.
i have three spare grey knobs from my machine drum and a spare big grey encoder wheel thingy i had to buy them from reverb!! anyways like the dude says they are hard to find