you're talking about these?
they're nice lightweight keys, but they do indeed have that one fatal flaw, which is why fender stopped using them.
contact fender directly; you should be able to get replacement screws and bushings for the ones that fell out. once you get them, take out the screws you do still have, drip some loc-tite 290 on the threads, and re-install them, quickly adjusting for your preferred amount of turning tightness (not
too tight).
once all the keys are loc-tited this way, you should have no further problem. i've had a set for years now with no problem after doing the loc-tite trick.