It can be found in the cave in the Mountain area. From the entrance, go to the southeastern corner and look for a place with a lot of plants covering the wall. But these plants only hide an entrance to a small part of the cave which is unlit. Inside that unlit cave, you can find a small chest which contains Corpsemaker.
First taken by the Picts as a war trphy from a dead raider, you found this Viking axe hidden in a highland cave. Its blade is beautifully engraved, its sturdy hilt marked with notches.