Yep - those screws snap off real easy. They are only there to hold the flipper onto the base - the base should "click" in - can you not get the screw out?
Ive just bought 90 off imperial screws for a 65 GTB machine - these might fit, ill check on some of my flippers for you - im pretty sure they are all generic.
If you purchase these from PBR, not only is 1 screw expensive ( well for a screw anyway) but they are slightly too long and you have to cut them down.
Let me check what i have, im damn sure that these screws are the same thread as those used to hold down relays, youll have to cut them down to fit, but thats not a real issue.