The US Military History Institute, Carlisle Barracks have two letters in their files.

George Martin

Title: 7th South Carolina Cavalry Regiment

USAMHI
RefBranch
laf & ca Sep 95
7th South Carolina Cavalry Regiment
Crute, Joseph H., Jr. Units of the Confederate States Army. Midlothian, VA: Derwent Books, 1987. Ref.
See p. 255 (1 photocopied page) for a concise summary of the regiment's service.
Confederate Military History, Extended Edition. Vol. 6: South Carolina. Wilmington, NC: Broadfoot,
1987. 931 p. E484C65.1987v6.
Contains numerous, scattered references to South Carolina units.
Daly, Louise H., ed. Alexander Cheves Haskell: The Portrait of a Man. Wilmington, NC: Broadfoot,
1989. 267 p. E605H37.
Sifakis, Stewart. Compendium of the Confederate Armies: South Carolina.... NY: Facts on File,
1995. p. 46 (1 photocopied page). E577S53. (Unit organizational history).
The following pertinent personal papers are in the Institute's Manuscript Archive:
Workman, Willie - MusickColl (Enlisted man's letters, Oct 21 & Aug 6, 1864)