The U.N. is a mammoth organization, with almost innumerable offices, agencies and publications. The Official WEB Site Locator for the United Nations System of Organizations is designed to help you find U.N. Web sites. It includes a section posting the most frequently requested U.N. publications. If that doesn't get you what you need, try the UN Legal Publications. United Nations statistics are available through UNdata.
A copy of the United Nations Charter is included in the American Jurisprudence 2d Deskbook.
A UN Web page provides links to all countries' Permanent Missions to the U.N., which can help you locate someone to ask questions about a particular country.
The United Nations Dag Hammarskjöld Library posts a research guide covering basic research tools, indexes, quick links to U.S. documents and training guides for U.N. information systems. See also Researching the United Nations: Finding the Organization's Internal Resource Trails by Linda Tashbook, which includes sections on finding U.N. personnel, issues, entities, operating documents, databases, research guides and treaties.
If you have access, HeinOnline provides a searchable collection of U.N. legal materials, including the United Nations Treaty Series, the Monthly Statement of Treaties & International Agreements and the United Nations Legislative Series. For the full list of titles and features, scroll down to the United Nations Law Collection in Hein's List of Collections.