Selected UN Resources and Research Tools: Overview and search tips for legal research by Wiltrud Harms, Reference Specialist for United Nations and Human Rights Law at the UC Berkeley Law School Library.
Official Document System of the United Nations(ODS) Most documents included were issued after 1992 but selected documents go back further.
United Nations Documents and Publications Microfiche Edition. Readex. Human Rights Segment 1986-2009, Basic Law Library Collection, 1986-2009. This would be a useful source for UN documents published prior to 1992. Law Library's updating ends in 2009.
United Nations Treaty Collection Includes UN treaty series and the League of Nations treaty series as well as the Multilateral Treaties Deposited with the Secretary-General database.
UN Treaty Series (Microfiche collection)
League of Nations Treaty series (Microfiche collection)