While playing as Darius, in the shrine under the castle there is a Save Crystal. Continue down the walkway you will fight a giant stone monster. Go left or right from that room you can find as many as four of these opponents. There is a good chance that they will drop a Palmira Ore, which sells for 1,000. They also drop Red Fruits on occasion, which also makes this location a good place to increase Darius' stats and equipment levels.