China doesn't make sense to me, if you had them since the early 80's. There were very few carbines around until the late 80s (88-89) to early 90's when Blue sky started bringing them in from Korea. Before that it was just some scarce NRA/DCM weapons and commercial like Alpine, National, Universal, and Plainfield. There just wasn't enough demand then for small humped parts. Guys like Bud Evers and Lonnie (Old Sarge) still had lots of vintage parts.
In fact, I had my FFL starting in 1982, and SELDOM saw a USGI M1Carbine, until the Blue skies came in.
BTW, the current "Old Sarge's drop zone" is not Lonnie