I neglected to answer all your questions the other day, and just remembered. Sorry.
There are several branch offices of the National Archives and Records Administration about the country. There is a branch in Kansas City, for example.
Frost's "Camp and Prison Journal" was reprinted in 1994 by Camp Pope Book Shop in Iowa City, Iowa. I think they still have copies for sale, but am not sure.
My own books I cited to you are "Guerrilla Warfare in Civil War Missouri, vol. 1, 1862," and vol. II, 1863 by McFarland and Company, Jefferson, NC. I am just completing vol. III, 1864-1865, and working like mad to get it off to the publisher.
You can access Frost's book and mine via Interlibrary Loan at your local library.
Sorry to be so long in responding.