Gwannas is a Bosmer armsman who initially can be found on the Fisherman's Isle located just outside the port city of Haven. If spoken to, he'll say, "Baffles me how we were driven out of the guildhall. It's not like our equipment is in poor shape or anything. I maintain it myself!"
After the city is liberated, he can be found at his shop on the upper floor of the Fighters Guild in Haven. [verification needed — as of today (26.11.17), the guildhall is inaccessible after the quest, Gwannas stays on Fisherman's Isle]