This is it! This will likely be my final post about the PEP22. Over Thanksgiving break, I finished the pistol. I bought some surface-hardening compound from Brownells and tried it out on some spare rivets, following the instructions on the canister. I tried quenching in both water and motor oil, but the compound would always bond to the steel in a hard mass. It was impossible to get it off without scratching the hell out of the metal underneath.
So I gave up on the case hardening. I've now put over 300 rounds through the gun and neither the sear nor firing pin is showing signs of premature wear. Those parts are easy enough to replace if they eventually wear out so I decided to leave them as-is. As for the trigger pin and sear pin, I do intend to machine new ones from better steel. I also tried using a letter punch set from Harbor Freight but it wouldn't produce even letters so I returned it.
Then it came time to blue the pistol. I ordered a jar of Oxpho-Blue cream from Brownells and started with the frame. It had some surface rust around the grip so I sanded that off. I cleaned it with air intake cleaner, scrubbed it with steel wool and then warmed it up with a propane torch (I read that this would produce better results). I did three applications and that seemed to work well. The inside surfaces of the frame were a pain to get to and I realized that I should have bought the liquid version instead of the cream. Here's how it came out: