What David said. I've also used an end mill to make a plunge cut into the breech face and then pressed-&-epoxied a bushing into the hole. Have made a small threaded insert for the Cadet's receiver threads that allows me to mark the new striker tip location from the front, concentric with the rifle's chamber.
A new replacement Cadet striker spring can be made from the spring from a 1903; actually 2 can be made from 1 1903 spring, it's long enough. I've found that the ends of replacement springs are usually slightly larger in dia than the remainder of the spring, and must usually be ground down very slightly to clear the inside of the Cadet breechblock.
Please be advised that although the Cadet striker springs are often weak and in need of replacement, a new spring even if much stronger is often not the complete answer to cratering primers. I've found that the Cadets almost always need a smaller bushed striker tip even more than they need a stronger spring, especially if using a cartridge with SR primers vs LR ones.
Regards, Joe
