Provost Marshall index online at Missouri Secretary of State includes "DC McKay" in Macon County. Entries in index suggest he is officer serving in some sort of provost marshall role, ie banishing a person, awarding money to someone. Dates: 11-15-1864. 12-2-1864. 1-17-1865.
This is most likely Dennis C. McKay. 2nd reg Cav and 11th msm cav Co F. Enlisted Feb 4 1862, Macon City, mustered Oct 12 1862 in Monticello. Started as a Lt, then to Captain. Promoted to Major Oct 26, 1863. IN 1863, Mo legislature made him part of 3-man commission to find the county seat of Lyon County. In April 1867 he was postmaster of Macon, leaving in 1871. In 1870 census, age 44, he had a railroad contract. Books indicate he was Director of Northern Missouri Railroad.
As to the True Democrat. Library of Congress has some info based on Description from Vol 1 no 13 (Dec 11, 1860). Published at Louisiana, Mo. Published by William G. Waite. A weekly. Library of Congress states only known edition is held by State Hist Soc of Missouri, Columbia.
HOWEVER, the library of Congress national holdings index is notorious for its omission. They only list info from cooperating institutions and from well-catalogued and indexed archives. The most recent update was based on those libraries that were fully automated with compatible software--which eliminated most smaller institutions. And LOC holdings index has not been well-updated for the explosion of materials now online. To find the original edition of the True Democrat you might try to Pike County Museum/Pike County Genealogical Society. Also try the libraries in Pike and surrounding counties. A similar strategy has worked for me; others will know which libraries have a treasure trove. The history of Pike County Missouri is online at Internet archive and you might find info on the True Democrat and William G Waite.
This doesn't answer your question about the CSA officer, but it may help you to find out more..
--Jean Dresden