UN Online Sources
http://www.un.org.pk/library/online-res.htm
The United Nations provides several excellent databases for UN research. However, none of these databases are comprehensive.
UN Official Document System (ODS)
http://documents.un.org/
Dates covered: 1993 - current
This is the official repository of UN documents and includes full-text images (.pdfs) of UN documents. The ODS covers all types of official UN documentation, beginning in 1993. Some older documents are added to the system on a daily basis. It includes resolutions from 1946 onwards. The system does not contain press releases, UN sales publications or UN treaties. Since January, 2005, this database is free to the public. The system allows for both simple and advanced searching. If you are unable to find your document with this system, try searching for the document in the AccessUN index (which goes back further than the ODS) or UNBISNET (the UN catalog). Then, use the UN document number to search in the ODS.
Once you found what you need go to a Depository Library
The United Nations Depository System
The United Nations facilitates the distribution of UN documents by using a system of Depository Libraries. Various libraries are given UN documents in exchange for making them available to the public. However, depository libraries do not receive all United Nations publications. Some documents are not made available to the public. Depository libraries receive "generally distributed documents and publications of the United Nations."
Do a google search "united nations depository libraries" for one close to you.