Dragonsmiths can be found in villages throughout the overworld. They may not seem friendly at first, but once you have slain a dragon, and when they have an anvil nearby, they can repair DragonRealm tools and armor.
Right-click the Dragonsmith with an individual tool or piece of armor to have him repair just that single item. Right-click with a Dragon Ingot to have him apply that ingot toward all DragonRealm items in your inventory. His repair ability will only consume one ingot at a time.