Meteor Metal Ore is found in a crater during a random encounter (which represents a reference to the saga of Superman, who was also found in a meteor crater by a human couple) while traveling on the roads between locations on the map. After a brief scene, go and collect the ore from the rock in the center of the crater. If you have the Warden's Keep DLC you can take the ore to Mikhael Dryden in Soldier's Peak after completing the Soldier's Peak quest.