I can't provide a specific answer, but if you can't find a replacement switch and assuming it's on the body of the lamp, you could open up the lamp and bypass the original switch by directly joining the wires running to it. Then find an easily available foot switch and install that on the power cable that runs into the base of the unit and use this new switch instead?
You may find that once you open up the unit, the original switch may be a simple generic part available online once you get a proper view of it.
Rupert, January 2020
