3600/4600 synth rotary switch

I am restoring 2 synths from the 70’s, an international 3600 and international 4600.
3600 is now working, but I need to source a replacement VCO Range switch, 2 pole 8 positions. The original was a 2 pole 11 position but 3 positions were never used.
Size is 3cm diameter.
The existing switch is so stiff I can only turn it when gripped with pliers.

Any suggestions regarding sources of replacement would be appreciated.

Suggestions on restoring would also be appreciated.