G-3 is the german designation of a spanish assault rifle developed by german engineer Ludwig Vorgrimmler in the 50's called CETME.
Basically the CETME was a spanish thing invented by a german who based his design on the Stg 45.
From what I've read, recievers for G3s were produced in Pakistan (POF), Iran, Turkey, Greece (Emco?), England (RSAF Enfield), and France (Manuhrin) ( also Norway?). They were also license produced in Germany by Rhinemetall (sp?).