"Why, Berath smiles upon you! What fortune, that on this turn upon the Wheel, you should find yourself before the finest merchant in all the Deadfire!"
This mysterious merchant appears in Port Maje Harbor, on the western wall of the market, when the "Unique Item Vendor" Berath's Blessing is enabled.
As of Patch 1.2.2.0033 - All Scavenger hunt items previously exclusive to Steam users are now for sale on the Vendor, unless you already have the items in inventory.