Go to any of the 3 people that give quests at the public soulforge in Ter Mur royal city, that give the imbuing quests (ingredients for powerscrolls). The mallet & chisel runics are a random drop from those quests.
In other words, you do the quest like you would for a Powerscroll, and a runic may result (can't remember if it replaces or is in addition to the PS)