This is possibly the most annoying achievement in the game. Try to do this as you do the collectibles and garage blueprints, as you’ll be travelling the map and every now and then an encounter should pop up, this will make your life easier in the end.
Types of Encounters
Now, the types of encounters that actually unlock supply points are:
- Vehicle deliveries.
- “Out of Gas” encounters.
- “Juggernaut” (This is technically also a vehicle delivery).
Do Not Bother Doing Hijack/Rebel Encounters. They do not unlock supply points.
Locations / Method
What you want to do, is check your map for Towns that do not already have a supply point in them. Fast travel to a town and start to wingsuit in and out of that town repetitively for about 5-6 times (you can see a little floppy disk icon in the bottom-left corner indicating when you enter/leave a settlement). if an encounter does not appear by then, fast travel to another town and repeat what you’ve done. you should pick a number of towns to alternate between to further increase your chances, and eventually you’ll get an encounter to pop up.
Hope this helps, and be patient. Good Luck!