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Good morning -
It looks like there are two catalog records of digitized materials that might have what you're looking for. The first is from RG 263: Records of the Central Intelligence Agency. This particular file unit contains lists of people interned in various European camps, including Camp Marcus W. Orr. The file unit can be found here: German Intelligence Service WWII, Volume 3.
The second file unit is again from RG 263, CIA Records, and a similar series about release of names of the people who were interned. This particular file unit is for one man, Anton Boehm, who was interned at Camp Marcus W. Orr, and other camps. The file can be found here: Boehm, Anton.https://catalog.archives.gov/id/26185524
While those are the only records I was able to find through our catalog, you may wish to contact Textual Reference at the National Archives in College Park, MD, to see if there's anything that might be of use. Their contact information is Archives2reference@nara.gov
Best of luck in your hunt!