Exile 1: Where to get piercing crystals?

[curi]

Where can you get piercing crystals in exile 1?

 

I know there is a shop with piercing crystals near Sulfras. Do any other shops sell them? Do any dungeons have guaranteed piercing crystals (I think Grim Cavern has one)?

 

I'm working on a speedrun and getting 2 piercing crystals could be useful but traveling near Sulfras is too far. You need to dispel two barriers in the tower of magi to get the blessed athame. If you learn dispel barrier you need to reach level 3 on a 6 int mage to get around a 5% chance to dispel there – it's unfortunately a 0% chance at level 2, so I'm considering getting extra xp I don't otherwise need or cutting a priest from my party to deal with this (level 5 mage spells + 9 int costs 59 skill points, so that should work at level 2, but there's no way for my primary mages with level 7 mage spells to reach 9 int at level 2).

 

I finished an exile 1 run in 54:29 yesterday with several minutes of time loss due to my mage being underleveled when I reached the tower of magi, and several more minutes of time loss on the grah-hoth fight.