Hello (Name Withheld)!
We appreciate your interest in our World of Warcraft art. For legal and competitive reasons, we’re not able to provide any 3D model files. However, you can find numerous screenshots and concept art pieces of Arthas and other Death Knights on our Wrath of the Lich King website
http://www.worldofwarcraft.com/wrath/index.xml. Thanks again for contacting us!