Check out the appendix to the latest edition of "Death From Above", the FG42's main reference book. Ken Keilholz has added a list of every known FG42, by serial number, and whether it is in a museum or in private hands. It's not a lot of guns. And if you email him nicely, he will tell you the history of your FG42, where it was captured, by who, and what happened after the war to your gun. I got mine last year, after a lot of angst as to "should I get this or not?", and its a really neat feature that takes a lot of the unknown out of the process.
Again, just for the type of questions here, "how many?", its really an eye opener...and if you ever get one, when you see the serial number of your particular rifle, it take a lot of the worry out of the transaction.