All major spaceports have external freight elevators, allowing ships that cannot land in a hangar, or are required to use a docking collar, to still access the freight elevator system from zero-G.
The cargo spindles of the space station should be relatively easy to identify
External Freight Elevators at Port Tressler
As you get closer, you should see the external freight elevators. If you get a trespassing warning as you approach don't worry, just keep flying closer and once you get to the right place that will disappear. You do not trespass in front of the external freight elevators, just some of the surrounding space.
The freight elevator kiosk that you use to raise and lower the elevator is on a platform overlooking the elevator on one side.
External Freight Elevator Close-Up
Different space ports may have their freight elevators in slightly different locations, but all of the external freight elevators have the same general structure: a large elevator with the kiosk to one side. Just keep in mind that the scale of the station might make the elevator look very small until you get up close!
Levski's external freight elevators are underneath the main landing zone. Fly through the hole in the center of Levski's asteroid to go below to the cargo spindles with the elevators.
Directions to the External Freight Elevators at Levski