The people at the State Historical Society of Missouri in Columbia, Missouri, would probably be the people to talk to about preserving your document. They have been very helpful to me in the past. Their contact information can be found on their website:
http://shs.umsystem.edu/index.shtml

By the way, for those who might be interested, archived issues of the quarterly "Missouri Historical Review" are now available for reading on-line.
The link is: http://statehistoricalsocietyofmissouri.org/collections/mhr.php
Many interesting articles about the Civil War in Missouri.