To cite papers, lectures, manuscripts, manuscript collections, and other unpublished items (often appearing as primary sources), visit Turabian section 17.7.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.
In the search, enter the keywords "unpublished scores" or "folios." Or, navigate to section 14.225