We do find him here.
F. M. Rembert enlisted as a Private in Company E, 3rd Mississippi Cavalry State Troops, July 6, 1864 at Gallatin [Copiah County] for a period of 12 months, the only card in his file records him present on his companies August 14 to September 14, 1864 muster roll [this is the one and only muster roll recorded for this company]
THIRD REGIMENT CAVALRY (State Troops) (Easterling’s)
Colonel--W. K. Easterling.
The designation of this regiment appears to have changed from First to Third Cavalry. The regiment was organized by the election of Colonel Easterling August 30, 1864, at Brandon.
Company A -- Capt. Speer’s Company (raised in Rankin County, MS)
Company B -- Capt. Thames’ Company (raised in Rankin County, MS)
Company C -- Capt. Barr’s Company (raised in Hinds County, MS)
Company D -- Capt. Harper’s Company (raised in Scott County, MS)
Company E -- Capt. Butler’s Company (raised in Copiah County, MS)
[Note: E. B. Rembert of the 4th Mississippi Cavalry, Co. F is recorded as a resident of Copiah County]
Company F -- Capt. Martin’s Company (raised in Rankin County, MS)
Company G -- Capt. Haneld’s Company (raised in Madison County, MS)
Company H -- Capt. Pierce’s Company (raised in Rankin County, MS)
Company I -- Capt. Owen’s Company (raised in Scott County, MS)
Company K -- Capt. Vinzant’s Company (raised in Rankin County, MS)
http://www.mississippiscv.org/MS_Units/MS_ST_TROOPS_CAV.htm