I bought a Datron Calibrator that has some some broken black switches (besides a lot of dirt and other issues).

Because these switches are hard to get and expensive, I decided to open a defective one:
one can see that the little "handle" is broken, were the spring should be attached.

to form a new "handle", I used a hot wire (0.5mm diameter) and put it into the plastic, so that it goes through the other side, melting the plastic.

After attaching the spring to the wire, the switch is ok again!

Maybe this helps someone, who cannot get/afford these switches.