Dear Mr. Jai Cho,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located three series Background Files to the Study, "Military Advisors in Korea: KMAG in Peace and War", 1951-1965 in the Records of the Army Staff (Record Group 319); Historical Reports, 1958-1960 in the Records of the U.S. Army, Pacific (Record Group 550); and Command Policy Files, 1953-1954 in the Records of General Headquarters, Far East Command, Supreme Commander Allied Powers, and United Nations Command (Record Group 554). These records are not yet digitized and available in the Catalog but may contain the information that you are seeking.
For access to and/or copies of these records, please contact the National Archives at College Park - Textual Reference (RDT2) via email at firstname.lastname@example.org.
We hope this is helpful. Best of luck with your research!