Well, the first few Orichalcum+ can be found if you get all the treasures from all the worlds. One is in Tron's world, one is in the World that Never Was (those are the only two I can directly remember at the moment - Tron's is near the Master Computer, and TWTNW's is right before you go into the Org.'s castle (by the save point, just go to your left, there should be a ledge)).
Everything else, you get by completing the mini games, certain quests, and the Underdrome Coliseum Cup.