Did you find the Chain Pull Puzzle room?? That is where the element is found.Here is the list of elements and where they are found:
Face of Corruption--the Blacksmith's room in treasure box where a skeleton lies motionless.
Idol of Darkness--in the Chain Pull Puzzle room with 8 gargoyles on pillars in which you have to solve this puzzle.
Paw of Contagion--Ardibran gives you that one if you find him in the clearing.
Tusk of Lust--pickpoocket it from Lysandra in the sewers or kill her outright to get it.
Light of death--from DeSoto's room in the tower.