To cite papers, lectures, manuscripts, manuscript collections, and other unpublished items (often appearing as primary sources), visit Turabian section 17.7.
Footnote example for score manuscript:
1. Author First Name Author Last Name, "Title of score," format, Year, Location.
1. Johann Sebastian Bach, "Cantatas. Selections. Seven cantatas by Bach, once owned by Mendelssohn," copyist's manuscript, [1700-1750], Department of Music Manuscripts and Books, Pierpont Morgan Library.
For information on how to handle items in folios and collections, view the Chicago Manual Online:
https://libraries.indiana.edu/databases/chicago
In the search, enter the keywords "unpublished scores" or "folios." Or, navigate to section 14.225