Soulstone can save the soul from being harmed, and can power constructs (if you give them a soul)
Most abundant source seems to be the Valuren Transcontinental War Facility.
Holy order high-level operatives use Soulstone necklaces to protect them from the damage to the soul that shadows can cause. The necklace must first be crafted by an expert jeweller, and then enchanted by holy order mages.