×the wind spell is in the ship frozen on the lake. Shoot the front in the eye with a magic dart and the mouth will open and a scroll will fall out.

As for "How do I find the dart spell" I'm not sure how you got this far without realizing that you already have it. It's literally the only spell you have when you start a Sorceress playthrough.

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Magic Dart: start with it
Flame Aura: Aurvendel gives it for free
Shadow: Aurvendel sells it for 20 silver
Channel: I don't remember, I think you get it for free? Or start with it? Or maybe Liff? It's the one that lets you cast from HP.
Sixth Sense: Plot, librarian thinger.
Shield: At some point when you're asking Aurvy for the eye, he'll need you to pick up Shield. It's in the Adventurer's Guild, and you need to ask the guy in the tower about it.
Blink: Win it from a svartalf.
Blessing: I think this was from Eitri, give him a tool (pickaxe, fishing net, tinderbox all work).
Disruption: Actually was this one Eitri? I don't know...
Arctic Wind: Dart the ship eye, like said above.
Frost Bolt: Now we're talkin! Cast Blessing on that stone on the path to Gastropnir keep. You may have to level Blessing a bit.
Lightning Bolt: I never got this spell. I'm told you get it from completing the "riddles" sidequest though.