I've had some luck with repairing originals. If you look near the base (where the connection tabs are), there is a welded seam in the plastic. I was able to cut through the seam and pry the end off, which releases the plunger and contacts. Clean them up, bend a little as necessary, then glue back together.
(My Stags don't have the third wire, but I believe the construction is very similar and the two contact switch is likewise hard to find.)
Another option might be a small wiring change. Use a single contact switch (of the right length) to activate a relay. The relay contacts can then supply power to the key light and warning buzzer.