Blake in Ars Magicana sometimes sells charms, though not as often as Kistandalius has them; Corinna or (less often) Mpenzak in Verdistis can also sell charms. Some people have found charms pickpocketing the castle soldiers, though I don't know what the chances of them having one are.
The lizards in the Verdistis sewers and Dark Forest can sometimes drop charms.
If you quick save before running your mouse over an item/chest/merchant or hitting the alt key, you can identify the item or trade with the merchant, then quick load to get different stats or inventory. This can be done repeatedly to get the best stats or specific bonuses on an item (save after finding good candidates) or looking for specific items (such as spell books or charms) from merchants. Don't waste too much time with this, though, it really isn't necessary to get the best possible equipment.
