A broken firing pin on a .22 rimfire is caused by A. simple fatique and or B. dry firing ( empty chamber.) This may also compromise the integrity of the breechface and chamber seal. There were countless retail firearms made, some by familiar names and not a few by long forgotten makers. Your piece can probably be put back into safe working order. Just remember that a .22 as introductory training firearm needs a decent degree of accuracy,site system and trigger; not to mention safety features. We certainly don't want to learn how to drive in either a Ferrari or Packard, fun as that may be.