It’s become increasingly challenging to find suppliers that stock the original C64 sized power switch for MB-6582 and sammichSID.
My standby had been the Retroleum shop: https://www.retroleum.co.uk/c64-misc-components-fuse-etc
But, they're not shipping at this time, due to Covid-19 impact
I managed to find two suppliers on eBay that seems to have good on-hand supply:
Suppler based in UK