Got a drill or a Dremel tool?
Make a new plunger out of a section of steel wire. Like, a nail of the correct diameter.
The end against the spring gets cut off flat, the end against the safety, gets a radius formed on it by spinning it in the chuck of the power tool, while shaping the round end with a file or some wet or dry sandpaper.
This sort of plunger makes a good substitute for a lost ball bearing. And is far less fiddly to install.
