LibAnswers

Physical copies are held in the Archives on the 4^th Floor of the Library.  

The Library of Congress also has some digitized slaves narratives.

https://www.loc.gov/collections/slave-narratives-from-the-federal-writers-project-1936-to-1938/about-this-collection/

And UNC Chapel Hill has digitized North American Slave Narratives from their Documenting the American South Collection

https://docsouth.unc.edu/neh/