I just purchased a Korean re-import with an Arlington Ordnance stamp on on the underside of the barrel. It has an Inland receiver and a Rockola barrel, with the remainder being a mix of USGI parts.
The exception is the sear which is stamped "RIA". I believe this is a M2 sear that was made by Rock Island Arsenal. The mystery part is the bolt. It is black and the only marking is an "H" on the left lug. Has anyone ever seen this?