There are two merchants in Neriak by the library that use defenders medals as currency. You used to be able to trade ulterian powder (or something similar) for coins to purchase things, but that is no longer an option as far as I was able to see. So how do I earn defenders medals so I can buy things like Magic Mouths and other house/appearance items?
Hidden in the long list of stuff on one of the NPCs is the option to buy defender's medal for either sovereign medal (current expac currency) or crusader's medal (???). So if you've been doing PQs and have spare coins, you're good.
The arcane gravel that you used to be able to buy things with are now used to make some of the house blocks and such. Cyrrena