You find NPC Porters randomly throughout the Central Region. They are groups of 2-3 characters walking around (they show up offline as well as online). They are Porters (delivery people) just like Sam and wear a white suit. They most frequently show up in the eastern half (right side) of the Central Region. They are most frequently encountered at the following facilities: Engineer, Craftsman, Elder, Film Director, Junk Dealer. However, you can also find them running around the wilderness. They do not go to the snowy mountain region.
Once you randomly encounter the Porters, make sure you give them as many likes as possible with the Touchpad. Then, open your Cargo inventory, equip one of your cargo to a hand, and lay the cargo on the floor in front of them. If they are interested, they will pick it up. Give them a few more items until they offer you one of theirs (they will stretch out a hand to offer it to you). Take their offering to get the “Any Porter In A Storm” trophy.