Dear Ms. Jones,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located and Registers of Letters Received, 7/1865 - 10/1870 of the Assistant Commissioner of South Carolina in the Records of the Bureau of Refugees, Freedmen, and Abandoned Lands (Record Group 105) that may list the letter you seek. The registers are part of M869. We also located Letters Received, 3/1865 - 6/1872 and the Registers of Letters Received, 5/1865-7/1872 of the Office of the Commissioner in Record Group 105 that may include the letter forwarded to Commissioner Oliver Otis Howard. For more information about the non-digitized records, please contact the National Archives at Washington, DC - Textual Reference (RDT1) via email at email@example.com. Include a copy of the letter from Letters Sent, 6/1865 - 1/1870 (M869, Roll 1) in your request as well as ask for a search of the letter from Reaves in both registers.
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 RDT1. We apologize for this inconvenience and appreciate your understanding and patience.
We hope this is helpful. Best of luck with your family research!