Samir Sanbar, A Guide to Information at the United Nations . You certainly will not be chastised for quoting United Nations statistics. If you are unfamiliar with the work of the UN, start with this US Dept. of State summary and the UN website . Unions is a meta-search engine of many UN websites and works beautifully.
Unions also offers a simple directory .
The UN Press Release database stretches back to October 1995. The search is flexible with a range of field searches, including a very good category search, available from the UN Press Release search page. Keep in mind these are press releases to UN activities, several thousand in total. The United Nations publish documents in two formats. Sales Documents have a UN sales document number in addition to a UN document number.