If you are looking for the "Immortal" experience specifically, you will likely need to install a community-made mod: Just Cause 2 on Steam
While "Immortal 3" is not an official title, the game received several official expansion packs in 2010, often bundled in the : Download Just Cause 2 - Immortal 3 PC Game 2010
: Offers a "Complete Edition" that is DRM-free and includes all official DLC. If you are looking for the "Immortal" experience
: The most common platform for PC gaming, which also hosts the official Multiplayer Mod. Download Just Cause 2 - Immortal 3 PC Game 2010
: Another reputable retailer where you can find the base game and DLC bundles. Official 2010 DLC Content