Free Trade is a quest you get from Adolphus, a violin-playing resident of the Bolmus Populi. Adolphus is located on a rooftop ledge near the entrance to the town. Aurora will ask for violin lessons but Adolphus will disagree. You will receive an Apple after that.
After you get this quest and item, travel to Capilli Village. Go right and enter the door with the pipe sign. When you enter you should find a teacher that you can talk to. He will say he's hungry and you will give the apple. In return, you get the Shovel.
After this, fast travel to the Old Monastery. Go left and you will find a Capilli complaining that he lost his shovel. You will talk to him and give the shovel, in return you will get the Lantern.
This is the last step. Travel to the Town of Bolmus Populi. Go to the right and go under Magna. Keep going under until you find a wish plant to your left and a rock enemy and blue chest to your right. Activate the wish plant and follow its orbs until you find the flaming spider. Go right of the flaming spider to the secret cave. Once you enter the cave there is a dropoff, go down it. Keep going down until you find a mining populi. You will talk to him and give the lantern you have. He will then give you the Gold Nugget.
Travel back to the Town of Bolmus Populi. Give the Gold Nugget to Adolphus. He will then give you 6 Strength Stardust.