Where are the Critical Bands?

[Islandi]

I'm starting to grind at Metal Island but I have only 2 Critical Bands. I read from another thread that someone managed to get 3.
Besides 1 from Treasure Chest and 1 from a boss drop, where else can we get Critical Bands?

[1oldtymer]

I don't remember, and you may already have stolen one Nils at Ohlu Tower. Someplace on the the net it says, "Normally, you could get only 3 Critical Bands, this way you will be able to have a fourth one."