So far I could only see one surcoat that let me wear it with my heavy armors.
I found it on the noob island where my orcs rescue team lives. I ran around after I got to level 15 and saw harder mobs there. They drop good stuff and even got a few side quests while exploring the remaining of the island. One of the chest they had on that island contained the item level 10 surcoat that I can wear with my knight armor set and it can be upgraded.
The rest of the surcoats I encountered in the game so far are only designed for robes.
I found every single skill book in the game besides Fire Strike and Battle Cry (both melee) from dungeons and chests with static items from the prologue and first chapter. I did see Fire Strike being sold by a vendor in the 2nd chapter.