I wont go into detail about the easily findable ones because you can just get the radio towers and they show up on your map im here to talk about the 4 that are not so easily found and dont show up on map or not always there.
1 – The first one that you might be having probloms finding is one from a quest giver at the very start of the game. After completing the hospital you will get acces to the open world. Once you have that you will want to go directly south of the hospital to a trading post. There is a quest giver there that gives you the quest “the first biomarker” do that quest and you will get an inhibitor for your trouble.
2 – The second one that dousnt show on your map is one in a safe in a dark zone right above the spruce windmill in “Lower Dam Ayre” the safe code itself can be found inside the dark zone while the safe is at the top of the dark zone.
3/4 – The final 4 that you does not always show on the map comes from the quest “cathedral” and will spawn an inhibitor case inbeetween the 2 towers of the “saint paul cathedral”. If you did the other quest line avoiding this one you will be forced to join somones game who has completed or is in that quest and the box will be inbeetween the 2 towers inside.