Don't look for FoS crit multiplier on ID as you will never see it, you can only get that one on reforges at lvl 10, 20, and 30. Find a stone on ID that has FoS damage, and Battle attuned power cost and level it up. Just search the AH every day, they are quite abundant
I'm a bit picky with my stone so if you ask me just be a bit more patient and look for one with good stats on it as well. +morale/21 will or fate/ or tactical crit rating would be nice to have. spending all of your time getting scrolls of empowerment and the right relics and then finding a better stone and having to repeat the process is never fun...