You can look up the coordinates of the traders in the prefabs.xml file of the map. Open the XML file with a text editor like Notepad++ and search for "settlement_trader".
To get to the map files you need to right click on the game symbol in Steam and select "Properties". Then go to "LOCAL FILES" and click on "BROWSE LOCAL FILES". Click on the folder "Data" and then "Worlds". Every map has it own folder with the name of the map.