I only found him on an Ancestry.com search on a Draft Registration document. No joy on either Federal or Confederate records on my databases.

U.S., Civil War Draft Registrations Records, 1863-1865 about Martin Hensley
Name: Martin Hensley Farmer
Residence: Salt River Township, Schuyler, Missouri
Class: All
Congressional District: 8th, 9th Sub. District
Age on 1 July 1863: 25
Estimated Birth Year: abt 1838
Race: White
Marital Status: Unmarried (Single)
Place of Birth: Illinois

Source Citation: National Archives and Records Administration (NARA); Washington, D.C.; Consolidated Lists of Civil War Draft Registration Records (Provost Marshal General's Bureau; Consolidated Enrollment Lists, 1863-1865); Record Group: 110, Records of the Provost Marshal General's Bureau (Civil War); Collection Name: Consolidated Enrollment Lists, 1863-1865 (Civil War Union Draft Records); ARC Identifier: 4213514; Archive Volume Number: 1 of 1.