The United Nations aren't the only body that is being simulated by students!
Moot Courts
If you're interested in trying out the judicial version of MUN, here are some references to court simulations:
ELSA Moot Court - WTO Simulation
European Law Moot Court Competition
Frankfurt Investment Arbitration Moot Court
Model European Union
The official MEU is open to citizens of the European Union only. However, you'll find MEU bodies in MUN conferences as well.