Bryce,
I don't find anything on a Captain A. B. Barnes in my lists of irregular officers of the Confederacy in MO, or in the lists of regular Confederate officers of James E. McGhee's 2008 book "Guide of Missouri Confederate Units, 1861-1865," Fayetteville, Arkansas: Univ. of Arkansas Press.
However, in Peterson, McGhee, Lindberg, and Daleen's 1995 work "Sterling Price's Lieutenants: A Guide of the Officers and Organizations of the Missouri State Guard, 1861-1865," publ. by Two Trails at Shawnee Mission, Kansas, on page 295 under the heading "Officers Whose Units Have Not Been Identified" is Third Lieutenant Andrew F. Barnes, and the footnote suggests that this A. F. Barnes "probably served in the 3rd infantry Regiment of the VI or the 6th Division." This was Colonel Franklin S. Robinson's regiment that formed in Saline County in December 1861 to travel "en masse" to Price's army then in the Springfield area, but Union cavalry forces in NE Johnson County, MO captured nearly the entire group on 19 December 1861 and sent them to a makeshift prison in St. Louis.
Indeed, in Eakin's 1995 "Missouri POWs" published by the author in Independence, MO, she lists 3rd LT Andrew B. Barnes of Cooper County captured by Union forces at Milford, MO (one of two or three names for Fitzgerald's Mill on the Blackwater River in NE Johnson County that cold winter day of 19 Dec. 1861, and sent to the military prison at Alton, IL. but with no entry in the remarks section to indicate what happened to the man.
I seem to recall that over 1500 southern men of the Missouri State Guard were captured in a lump at that mill, and many of them had enough of the military experience thereafter, and did not render any further rebel service thereafter. However, some of these former Yankee prisoners from 1861 came out of the woodwork during Price's Raid and served the cause one more time.
As for "Captain Orchard" there was a clan of Orchards in Dent County during the war. In Eakins' "MO POWs" (cited above for Captain A. B. Barnes as a POW) we find Private George W. Orchard of Dent County who was captured in Springfield, MO 17 March 1862, and subsequently sent to the Alton, IL prison, with no mention in the "remark" section as to what became of the private. In my 2014 "Guerrilla Warfare in Civil War Missouri, Vol. 4, September 1864 to June 1865" I mention on page 276 how a Union patrol of the 13th MO Cavalry tracked a group of guerrillas across part of Shannon County in south-central MO (a few miles south of Dent County) in April 1865, and captured two bushwhackers. The two prisoners claimed they had earlier been part of Captain Jesse Orchard's company in Confederate Colonel Thomas R. Freeman's cavalry regiment from that region. The Union patrol claimed they later had to shoot the two guerrillas as they tried to escape. My source for the Union pursuit of these southerners is "O.R." Vol. 48, part 2, page 154.

I hope that helps. Anything else? Bruce