Here is a map of Point Lookout. Simply visit the locations. If you are past Level 20 and select the "Explorer" perk, then all the locations will show up on your Pip-Boy. You still have to actually visit the locations, but at least you can find them a little quicker.
Also please note that there are 4 locations that show on the map but are NOT required for the trophy. Here they are:
-Sub Recovery Site