For years, the DLC characters—essential to the full roster—were impossible to obtain legally. If you are looking for the pkg files or trying to understand why this content vanished and how it returned, here is the complete breakdown.
While it saw a brief re-release in 2010, it was permanently delisted from the PS3 store on December 31, 2010. The 2016 Re-release: marvel ultimate alliance 2 ps3 dlc pkg