Long Ranger,
The "standard fix" for a broken firing pin on a Martini Enfield Rifleis to have a short piece of drill rod of the proper diameter soldered into the firing pin. If you an't do this yourself or know a reasonably skilled gunsmith (not a parts-changer) I suggest you contact Brian Dick
in Edgefield. About Us
Brian is very knowledgeable about Britishfirearms and easy to work with.