Without looking it up, I think the Korean returns started in the late 80's or early 90's sometime. My understanding is the Korean military had their own sources for replacement stocks and a few were on the returned guns. Blue Sky Productions, Arlington Ordnance , and seems like there were others that imported M1 Carbines and M1 Rifles during that time period. I'll see if I can find an example of a Korean stock on eBay for comparison. - Bob
Added Later:
There's several similar stocks on eBay right now with that type wood. Interarms has a couple of new ones. Here's a link to a handguard that's likely Korean - look closely at the grain of the wood:
https://www.ebay.com/itm/WWII-M1-CAR...6/154071750359
Heres a stock:
Attachment 113822