If you haven't unlock river bank yet. You may find him by take a short break at a way point between your hut and Bareshade. (You can also find Torben (the merchant) with this too.) (RNG)
If you have been unlock river bank. You may find him by take a short break at river bank. (You can also find Torben (the merchant) with this too.) (RNG)
If you have been unlock Northcrest. You can find Gunnar by roaming around in residential area daytime, and also find him at the inn by public bath. (Both of this way are RNG.)
If you have been finish Bareshade's expansion event at living aspect, there will be a house next to your Bareshade house. You can find both Torben and Gunnar at that house in certain day. (There a chance that you can meet only Torben. Just leave his house and enter again.)
Another thing you should know is if you already fight him at fisherman village and you choose to fuck him. You will got a black heart with him that make him avoid to meet you and you cannot have more interaction with him.
I don't know if this can help since you don't tell any detail of your game process (like quest log or something). You can tell me if you try all those and you still cannot find him.