You didn't find his records as he is recorded as MaTTney. The only information I could find of his unit is the book noted at the website below.

George Martin

C R. Mattney

Enlisted as a Corporal
"F" Co. TX 13th Battn Cavalry

C. R. Mattney [sic], age 29, enlisted as a Corporal in Company F, Waller's Regiment Texas Cavalry Battalion, August 27, 1862 at Vermillion, Louisiana, February 29, 1863 recorded as absent "Detailed with horses by order Gen'l Magnider, no further records

See: http://openlibrary.org/b/OL4919638M/West-of-the-Mississippi-with-Waller%27s-13th-Texas-Cavalry-Battalion%2C-CSA.