Ken,

If you haven't already you may want to sort through the finding aids of The Pearce Civil War Collection - Navarro College

http://www.pearcecollections.us/page.php?cat=Collections%20and%20Research&id=2

Also, see:

http://www.ozarkscivilwar.org/archives/3343
Joseph H. Mason Papers
Contributed by the Wichita State University Special Collections and University

http://www.lib.utexas.edu/taro/tslac/40040/tsl-40040.html
Sam Bell Maxey papers
...one letter from Headquarters, District Indian Territory, Fort Towson, Choctaw Nation, June 2, 1864; a bound ledger of 431 copied letters from December 26, 1863, to September 20, 1864, Headquarters Indian Territory, while Maxey was serving as a general in the Confederate Army;

Confederate Research Center, Hillsboro, TX