Hello Nathaniel,

Have you seen the resources at the Eisenhower Library? I found this finding aid for you: https://www.eisenhowerlibrary.gov/sites/default/files/finding-aids/pdf/world-warii-participants-and-contemporaries.pdf

It has one entry as follows:

TONKAWA HISTORICAL SOCIETY

Volume: -1"

Papers [printed account of POW camp at Tonkawa; includes stories by two German officers who were interned there (English translation of original German account); booklet forwarded by Joe Todd of Bartlesville, Oklahoma]

If you haven't read that, I hope it's helpful,

David

Dear Nathaniel,

Thank you for posting your request to History Hub!

We have searched the National Archives Catalog and located 150 results for the search term "Tonkawa" in the Records of the Bureau of Indian Affairs, 1793-1999 (Record Group 75). A majority of these records are located at the National Archives at Fort Worth (RM-FW). For more information about these records, please contact the National Archives at Fort Worth (RM-FW) at ftworth.archives@nara.gov.

Due to the COVID-19 pandemic and pursuant to guidance received from the Office of Management and Budget (OMB), NARA has adjusted its normal operations to balance the need of completing its mission-critical work while also adhering to the recommended social distancing for the safety of NARA staff. As a result of this re-prioritization of activities, you may experience a delay in receiving an initial acknowledgement as well as a substantive response to your reference request from National Archives at Fort Worth (RM-FW). We apologize for this inconvenience and appreciate your understanding and patience.

We hope this is helpful!

Alicia Gabriel

While I do not have an exact lead to a primary source, I may suggest an expert in the field that can point you to some sources.  You may also give his biblio list in published books or papers a look for possible connections.  Dr. Antonio Thompson has published "Men in German Uniform: POWs in America during World War II" along with many papers on the subject.  Just a thought,