How do you get 13 orichulam in Kingdom of Hearts 2

It is "Orichalcum". And you get them from treasure chests or the "Rare Heartless" known as a vendor thing. Really, it's very small and looks like a tiny mobile gumball machine. The only way to get the "prize" is to use the given reaction commands. It may not always give it to you, because it may give you something else. The way to know if there IS a rare Heartless in an area is when you enter the area at the top where it gives you the information it will tell you there is a Rare Heartless there. One of the only places I've found them (once there was two of these Heartless!) was the Agrabah Bizarre beside the gates to exit to the save point by the Cave of Wonders and the Ruins--if you haven't already gotten the ruins, I can tell you they are not fun, but you need to get through it to finish Agrabah. Good luck!