The TARS101 is described in the game as:
A 4.5-5.5x advanced combat optic.
You’ll find this in eastern Pucara province in some hilltop ruins in the middle of nowhere. A “Sicaro Leader” side mission is nearby. The accessory case is inside one of the buildings.
There are five sicarios plus the sicario leader here – easily managed with a sync shot. You then have to kick down the door to get inside to the accessory case.
The TARS101 is a nice scope, and has a good high zoom. If you’re in the area or it’s still early in the game for you, this will probably be the best scope you’ll collect for a sniper rifle until you get up to Koani to get the TX5i, which is just a clearer scope and a bit nicer to use in my opinion.
Until then, this is a great option if you snipe.