Iridium Ore is a crafting material added by IndustrialCraft2.
This ore can be found in dungeon chests, village chests, and mineshaft chests (extremely rare). It can also be created inside of a replicator using UU-Matter from a Mass Fabricator. Keep in mind that the replicator requires a cd with the iridium pattern on it, so you're going to need to find some anyway. Iridium Ore can be used to make Iridium Plates, which can be used to create some useful items such as Quantum Armor, and the iridium drill.