I found the one behind a tree on the immediate west area, and the one surrounded by shadow peeps on the far east. Couldn't find anywhere else to explore.
Ah, I see what's going on. We didn't get to add the extra area to v0.1.0, so the third key was missing.
You could try out v0.1.2, which just removes the third key slot, or v0.1.7, which adds the extra area (and also fixed the sounds).
