This guide shows locations and clues to all 3 bunkers in the side mission in Episode 3: Wintermute.
Beware: This guide may include spoilers from chapters of Episode 3, main events and locations. I would recommend progressing the story first before reading through this guide.
Start at the House opposite Community Hall, there is a body and a backpack that gives you your first clue.
It leads to a bunker up North. It's the same route you want to take when going to the plane crash site.
This area is mainly known as the Abandoned cache in Survival mode, near a rope climbing spot to TWM.
Note from the first bunker will lead you across the area, passing the Farmstead and Molly's Barn.
The same situation as above: note you found in the previous Bunker will wrap around the map back to the Community Hall, cross the brigde and keep walking behind a house on your right, up a slope and around a rock you will find your final treasure. With some very, very, sweet loot.