The best way I know of getting purify runes is to take a high 20's, low 30's character into Ystra and kill ferrets, higher level ones preferably. The higher the level difference, the more likely you'll get runes instead of other drops and they drop purifies like candy.
As I once walked the path of the Wicked, I now pay my penance in Purgatory.
Abandon hope all ye who enter.
