You measure the inside and outside diameter, the diameter of the wire, the number of coils, and the overall length of the spring when uncompressed.
Then you stick the spring into your pocket and head for a bolt supply place, hardware store, or the junk drawer, and dig around until you find a match.
If you are really hard up, you can buy spring wire from a machine tools supplier, and wind your own. You will need to sort out a couple things, like the diameter of the mandrel to wind it around (smaller than the final diameter) and the method you use to wind it (eg. you can get a special spring winding tool, or you can make a substitute that will work for one or two, or it can be done in a lathe or drill press).
I would try a spacer washer first. File or grind the broken off end to have it sit flat against the washer otherwise the crooked seating will push sideways on the striker some. May or may not make a difference, but it's easy to do.
Is the Lloyd Gun Show done already? Usually a pretty good collection of used gun parts dealers there. Worth collecting a few phone numbers while out and about at the shows.
You should have .060" or so of firing pin protrusion, maybe a bit less. I would suggest getting in to the back side of the breech block with a copper or brass tool and dig around where the firing pin fits against the back side of the breech face, for pounded hard mung, which might be present there. Rimfire mung can get pounded solid and prevent the pin falling as far as it should. But more likely the spring will solve the problem, unless prior hands have had at the various parts.
Cheers
Trev
