Jimmy, I appreciate it's not as much use to you now, but I mentioned before on the other 501X thread a good place for stainless steel screws:
http://www.stagonset.co.uk/fasteners...=2375909_23212
Just use the parts summary in the back of the manual and away you go! They only do down to M3, but that's the vast majority in the kit. I got a set + spares for around £15 (inc P&P) and you should receive them within a couple of days. I've not come close to stripping a head yet, either on the Tamiya or my Pred.
Is there anyway way you can file/cut a slot in the head of the screw to get it out with a blade srewdriver?