Natalan Copper, the Natalan Sentry is on top of the chest.
U'ghamaro Silver, the U'ghamaro Overman is on top of the chest
U'ghamaro Brass, the U'hamaro Ashman is at the entrance of the corridor leading to the chest room
U'ghamaro Copper, the U'ghamaro Ashman is in the little room west of the chest room
U'ghamaro Gold chests ar in that little room behind the widest room in the south east and the boss pops at the entrance of the corridor leading to that room
Happy hunting :D