Ashen

I'm unsure what counts as a "Kol's armor," but I was able to find five armors in the DLC areas and the achievement popped upon picking up the fifth, so I assume that you need them all.

There is no in-game map other than in the starting area, so I'll do my best to describe their locations.

1) The Fallen Noble: Found on a corpse directly north of the first Ritual Stone behind a boulder.
2) Moppet of the Whispers: After progressing through a large cavernous area, you'll end up outside where you need to jump across a gap to progress. Enter the next cave and follow the path down some steps, hugging the left wall. At the bottom around the corner you'll see the armor on a corpse:
3) Mantle of the Tinker: From the Alag Riak Ritual Stone, slide into the Bral City. Make your way up and to the left towards the huge building that leads to Watcher's Roost. There is a single bridge that leads to it- to the right of the base of that bridge is an alcove where the armor is visible on a corpse:
4) Spirit of the Wild: After killing Gravkis the Hollow, enter the large building to find the final Ritual Stone. Just beyond is Watcher's Roost, an open area with two caves on either side. Go into the second cave on the left, kill the two enemies inside, and jump across to the platform in the back to find the armor on a corpse:
5) Ancient Vision: Follow the linear path from the final Ritual Stone towards Riak. After reaching a ledge overlooking a shield/spear enemy, a healer, and two crabs, you'll jump across a gap and go through an area where you encounter some shadow dashers. You'll then reach an area where you jump over a yellow stream, then turn a corner and immediately get attacked by a large normal enemy, then a smaller normal enemy and a crab. Before jumping across the yellow stream to continue on, look left to see steps leading up along the wall. There will be a crab halfway up and two shadow dasher enemies at the top (one of which is sitting down oblivious to you). The armor is on a corpse atop this ledge.