This order in the Official Records shows the table of organization for the forces in Arkansas at this time.
SPECIAL ORDERS,
HDQRS. TRANS-MISSISSIPPI DEPARTMENT, Numbers 39.
Little Rock, Ark., September 28, 1862.
http://ehistory.osu.edu/osu/sources/recordView.cfm?page=883&dir=019

Camp Nelson web sites
CAMP NELSON CONFEDERATE CEMETERY
http://www.couchgenweb.com/civilwar/camp_nelson_cemetery.htm

http://members.aol.com/SMckay1234/campnelson.htm

For Texas units at Camp Nelson:
Walker's Texas Division, C.S.A: Greyhounds of the Trans-Mississippi by Richard Lowe
The Campaigns of Walker's Texas Division By a Private Soldier by J. P. BLESSINGTON

Other sources for Texas units at Camp Nelson:
Peculiar honor : a history of the 28th Texas Cavalry, 1862-1865 Johansson, M. Jane.
The Spartan Band: Burnett's 13th Texas Cavalry in the Civil War by Thomas R. Reid

12th Texas of Infantry
Order of Battle for Walker's Division October 1862
http://www.geocities.com/rebel12th/history.html
This is how the division was organized in October 1862.

First Brigade
Colonel Overton Young
12th Texas Vol. Infantry
13th Texas Dismounted Cav.
18th Texas Vol. Infantry
22nd Texas Vol. Infantry
Halderman's Battery Second Brigade
Colonel Horace Randal
28th Texas Dismounted Cav.
11th Texas Vol. Infantry
14th Texas Vol. Infantry
Gould's TX Infy. Battalion
Daniel's Battery
Third Brigade
Colonel George Flournoy
16th Texas Vol. Infantry
16th Texas Dismounted Cav.
17th Texas Vol. Infantry
19th Texas Vol. Infantry
Edgar's Battery Fourth Brigade*
Colonel James Deshler
18th Texas Dismounted Cav.
10th Texas Vol. Infantry
15th Texas Dismounted Cav.
25th Texas Dismounted Cav.