Quick-save the game beside Kistandalius in Ars Magicana or Corinna in Verdistis, before hitting alt, running your mouse over them, or talking to them. Then trade with them and look for rings or amulets with a bonus to Pickpocket or Lockpick; quick-load if they do not have anything. This may take awhile looking for something specific; I just kept an eye out while sorting / trading loot and found a amulet with Pickpocket before I needed it.
