Old enough to have money
Try egunparts
In older guns....and most guns that people think of when they think of a handgun or rifle, there is a "hammer" and a "firing pin". When the trigger is pulled, the hammer is released and it strikes the firing pin which in turn strikes the primer on the cartridge, firing the round in the chamber. With a striker fired gun, there is no hammer. The striker, which is basically a spring loaded firing pin, is released, doing the job of the firing pin and hitting the primer on the round in the chamber. These guns have become very common, and you will find examples of a striker fired system in all Glocks, Springfield XD's, S&W M&P's, Taurus 24/7, etc.
Find a good gunsmith or machinist
www.leesgunparts.com I have new firing pins for that model. sales@countrygunsmith.net
A firing pin that is mounted on/in a hammer
Firing Pin Block
try numrich.com
Numrich Arms probably has them, but this is an item any gunsmith should be able to manufacture.
http://www.remingtonsociety.com/rsa/service
Like it says, the firing pin rotates as the action cycles.
What should Firing pin protrusion measure?
Check the gun stores in the yellow pages