Frost Dragon Armour is the next lot of armor but is a little easier to find because it can be found in lvl 5+ Mountains instead of the usual Lvl 7+. When your Dragon Keep is Lvl 8+ and you have all the armour your Frost Dragon will wear it and will be able to participate in attacks!

Note:You can find the Frost Dragon egg and armor before you have your Spectral ruins but you need the Spectral Ruins to build the ice outpost.