Dear Mr. Troy,
Thank you for posting your request on History Hub!
Custer commanded the First Brigade in the First Division of the Army of the Potomac’s Cavalry Corps. It is often referred to as the Michigan Brigade. We searched the National Archives Catalog and located 3 record series created by the brigade, 10 record series created by the division, and 23 record series created by the Cavalry Corps in the Records of U.S. Army Continental Commands (Record Group 393). For more information about these records, please contact the National Archives at Washington, DC - Textual Reference (RDT1) at Archives1reference@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 RDT1. We apologize for this inconvenience and appreciate your understanding and patience. Please see https://www.archives.gov/coronavirus for the most
current information about NARA’s response to COVID-19.
Many records relating to the Civil War have been published as The War of Rebellion: A Compilation of the Official Records of the Union and Confederate Armies in the War of the Rebellion which is available online at a number of websites, including Ohio State University's eHistory. There have also been numerous biographies of Custer published, as well as books about the Battle of the Wilderness and the Overland Campaign. One particularly good book is The Battle of the Wilderness, May 5–6, 1864 by Gordon C. Rhea which includes some mentions of Custer. You should be able to locate additional books online, through retailers, and through your local libraries.
We also suggest contacting the Fredericksburg & Spotsylvania National Military Park’s Park Research Library.
We hope this is helpful. Best of luck with your research!