In the mundane world, arsenic can be found in everyday objects such as rocks, soil, water, and even air. It is in all practical terms  a natural element, and not harmful to those in the world. But for those practicing the art,  who wish a purer, more potent form, for research and potion making, we have found a truly far superior grade. 
 
The purest form of arsenic can be found by pulverizing the kidney stones of stone trolls found in the Grey Highland Range to the east of Avalon. After careful negotiations, with a few tribes of stone trolls, we have secured the ability to acquire these kidney stones.  Once we have secured them, my apprentices begin the process of breaking down the stones, extracting the toxins, and purifying them. Corked and sealed in a vial, to preserve its potency. Sufficient for all magical potions, magical studies, and spell components.