You can probably get the gauges from Brownells. Remove the extractor, clean the chamber and bolt face as best you can, then try to close the bolt with the headspace gauge inserted (use hand pressure, not a hammer, to determine if it will close or not). Go should close, NoGo should not (if its NIB; on C&Rs, its personal choice if you use NoGo or Field), and if it closes on the Field gauge get that gun to a gunsmith immediately.
Most C&R collectors that I know use only a Field gauge. If it closes on loaded ammo, thats good enough for Go, and the Field gauge is the absolutely max that a chamber should be.
Kharn