I wish I had better news for you. I think the once-healthy supply of MG1 parts has dried up. The only upside that I can think of, is that even in moderate condition, the concertmate can still pull a good resale value. Maybe sell it and buy a used sub phatty or little phatty?
I ordered a kit of sliders and knobs from a place called “Technology Transplant” (Hong Kong?) a couple of years back. They then told me they couldn’t fulfill the order and refunded my money, after I found my emails to them chasing up the order kept bouncing back. After doing some googling it seems I got out of this OK as it sounds like they were a pretty suspect operation. They now seem to have disappeared, but if you come across them in your search tread carefully.
This is a few years late, but if you’re still looking there’s a couple options out there. I bought a set of switches and sliders from these guys and the quality is pretty good:
I went through the tedium of taking apart and cleaning all the gunk from the pots but the resistive strip was beginning to rub off, so I was happy to find a decent replacement. Another option is from Syntaur: