The following 4 Brocks were in the Texas Brigade.
They were all in the 6th TX Cav Regiment.

Company C, Capt. Smith recruited mostly from Collin and Dallas Counties.

Leonidas Brock PVT

Company E, Capt. Jack Wharton recruited from Van Zandt County.

John H. Brock, Sgt
James R. Brock Farrier
Newton V. Brock Pvt

I did not find any Brocks in the 3rd, 9th or 27th(Whitfields Legion) Texas Cavalry Regiments, CSA.