I like this topic so ill post back
Each power stones are drop by specific monsters. Aside from MOs,World bosses and treasure chests, some rare and map bosses drops them. (Average probability of drop rate is of 5% unless you are really lucky. For treasure maps, probably 10% or lower cuz i got 1 stone in 10 hunts) ill post semi-completed list on or before the maintenance this week
Too bad I can't verify the drops from lvl 60 up
but mostly they can be bought from NPCs that requires reputation. I'll post it here.