I had found 2 of the barrels prior to meeting Sherri. A radio dialogue started after the first barrell was found, saying she would pay for finding the rest. When I spoke to her in person she said "Oh you already found one." The 2 I found previous to meeting her were in Silver Lake (at the Tanami Residence Dredge/Ship and the barrell just west of that location). When I first started my search to acquire all barrells I noticed I was only showing 6/15 after acquiring all barrells within Silver Lake(instead of 7/15). I revisited each location 4 times prior to moving on to the other locations west of Silver Lake. I have restarted my xbox as well. There has been no magazine/map for purchase from any vendors in the area, as mentioned in a prior reply. HELP lmao.
Not sure why it wasn't showing up, but the map was purchasable at a Boat/plane shop(specifically the one at the Tanami residence, if it doesn't show up for at any other shop for anyone else). The map shows an icon on my big map near the mini island near Drubman Marina....a place I dove at 5 times. Will edit with a success if the barrell is now there for some reason?
**Success!**
Barrel was where I was looking, not too sure why it wasn't there before. Probably I was just missing it.