Christopher Newport University has several primary sources digitally online (I’m not sure if it will let me link here but I’ll try: https://cnu.libguides.com/c.php?g=23197&p=136481 )

Also Library of Congress does have limited items up (I found maps the other day) so double check there just in case.

Dod is funded. I would reach out to the Military History Institute (Carlyle Barracks PA). You may also have some luck contacting the library at Virginia Military Institute to see what they may have primary source wise. Maybe the American Civil War (formerly theMuseum of the Confederacy) in Richmond Va can also assist.

Have you checked with the Sons of the Grand Army of the Republic or the Sons of the Confederacy? At least they may be able to point you in a direction for primary sources (privately owned archives near your location, etc). Local historical societies of towns that had men in the battle may have letters, too.

Good luck!