Best place to farm Power Crystals?

Duals, harps (blue), the blue herb town pirates, qualm monks, qualm chiefs, and vikings are some of the most commonly hunted monsters that drop power crystal ores. I would continue doing qualm chiefs if I were you, at least you get some exp and chances at time pieces.

I usually get a Piece of Time within two hour of killing mobs. But I spent a nice solid 4 hours with 2x drop at Qualm 5 with no Pieces of Time.

I suppose my option aren't looking too good =/