When I was working at Brisbane Cabs, we were fairly pally with the local Ford dealer, because in brissy most cabs are Fords. So in my case there it was just a matter of ringing the parts guy and quoting the VIN number. Assuming of course that the radio in hand was the original radio for that car. You can with much anguish get the security number by quoting the radio's serial number.
We used to engrave the security number onto the radios as they used to get swapped between cars, usually if a cab was written off then the good radio out of it would get swapped into another car. If you look on the edge of the sunvisor of an ex brissy cab you will find several 4 digit numbers written and scribbled out.
I suspect that in order to get the security number now there would be some rigarmaroll involving your grandmothers maiden name and a masonic handshake.
Old habits die hard so when I pulled the radio out of my Forte, I engraved the security number onto the radio and wrote the number on the edge of the drivers sunvisor.
You don't get many goes at lucking the code before the radio locks you out for a way long time.