A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Unpublished government documents
Notes-bibliography style: citing specific types of sources
Part II. Source Citation

If you cite unpublished government documents, follow the patterns described in 17.6.4.

Most unpublished documents of the U.S. government are housed in the National Archives (NA) in Washington, DC, or in one of its branches. Cite them all, including films, photographs, and sound recordings as well as written materials, by record group (RG) number.

The comparable institution for unpublished Canadian government documents is the National Archives of Canada (NAC), in Ottawa, Ontario. The United Kingdom has a number of depositories of unpublished government documents, most notably the Public Record Office (PRO) and the British Library (BL), both in London.