The United Nations website has tons of information for students in Model UN. Don't overlook their site!! It can be found at: https://www.un.org/mun.
The "Home" page on the guide (first tab) has information about setting up a Model UN team. The "Resources" page (second tab) has tons of research information you can use to prepare for your practice sessions or competitions including Sample Documents, Model UN Guidance, Research Resources, Core Documents, Videos, and a Secretary-General's message.

Under Research Resources, you will find:
SERIOUSLY, you want to check out the Model UN website and use these resources!! There's even a UN i-Library linked!