As Yonhap reported on September 16, the US has released more documents related to the Gwangju Uprising, this time from the Jimmy Carter Presidential Library. The majority of this material is available at the US Embassy in Korea's website; six pdfs full of material were uploaded there under the names "CARTER PRESIDENTIAL LIBRARY DOCUMENTS" on September 17. There are also a number of cables there uploaded on July 6 this year that I had been unware of. Another set of documents from this collection can be found here at the May 18 Archives website; they're contained in a zip file (look for "파일: 카터 기록관 신규 공개자료.zip") with various folders of material, including one folder of cables related to the immediate aftermath of Park Chung-hee's assassination and another of cables related to Kim Dae-jung's trial.
(Hat tip to Yongju Choi, who unearthed the Jimmy Carter Presidential Library documents.)
Another Gwangju Uprising-related document I found online was "When It Wasn’t Fun (The Kwangju Incident Of May, 1980)," an account of the uprising by American missionary Charles Betts Huntley, written in 2005.
And, while we're (vaguely) on the topic of the fifth republic, here is a Korea Times article titled "Intercountry adoptions 1985-92: A numbers game for Korea's national image," which examines overseas adoption of Korean children and its relation to the policies of Chun Doo-hwan.