The jewellery dealer in Aleroth can sell charms, as can the guy in the ministry building there after you do the associated main plot quest (though you may want to be level 30 or so for that). The head guy on top of the harbour building can tell you what is needed to get to Aleroth, if you don't have access yet.
The jewellery dealer in the bunker and trader in the Red Hammer tribe cave can have charms. Sassan and the merchant in the dragon cliff castle can have charms (not as frequently, I don't think, but I didn't check them very often, mostly just selling them loot until they were out of gold).
The mine tower is in Broken Valley (IIRC opponents there are level 28/29 after the battle tower), where you got the cutscene approaching the quarry entrance for the first time (around level 12) of them blowing up the main entrance to the mine.
