It seems, it's not available at the moment. If you'll check the collections section and hover over the Yorn area, the tooltip says "There are no collectible points yet."
EDIT: So here is the path to track the source of this collectable item. You get it as a reward for the ocean adventure shown on the "Ocean adventure reward tab". Then on the adventure's page you can see the source item, which you have to get to activate it. And on the source item's page you can actually see, where you can get it from.
In this case it would be this Secret Map, which is sold by Spearfish Hunting Guild Vessel.
I'm still not sure, if it's available in the game at this moment or not.
In the collectible section there are Maps, where it says something like "[Exchange]Harbourname - Shipname", which i found. On this one it only states: "[Exchange] Yorn".