They're timed unlocks based on the Ubisoft servers. To find them, you first need to see where the Pivots you already have are located and pick them up via the Pivot map. Then:
1. You look at your list of Pivots to see which one has been revealed next.
2. Warp to the place where said pivot is.
3. Once there, you can place one of the three pivots you have from the start in the location you're standing. The idea is to place pivots to triangulate the location of the next pivot you need to find. It works like this:
3a. Place Pivot A on one end of the map. Quick travel to an opposing end and place Pivot B there. This should form a line across the Pivot map. The highlighted green area is where the Pivot you're looking for can be.
3b. Hoof it to a location inside the green area mentioned before and place Pivot C, which should form a triangle. If the highlighted area is inside it, then the pivot you're looking for is inside that triangle.
4. Continue to make the triangle smaller until you only have a small area to search and can easily find the pivot.
5. Wait for the timer to run down on the Pivot list so you can find the next one.
Alternatively, what I just typed in video form:
Click.
The more pivots you find, the easier it becomes to find the next one since you have more pivots to use for finding them. the whole thing is dumb though.