The EXPS & G33 is described as:
A red dot sight plus scope. Toggle the scope while aiming.
This scope can be found just south of central Monte Puncu province, on a hilltop. A “Food Drop” side mission is nearby to steal a helicopter. The accessory case is on top of a crate next to the helicopter.
The terrain makes this difficult to approach. You could jump from an aircraft, but I took a motorcycle until I was close, then approached on foot from the south west up a path. There’s a sniper in a tower which I shot first, then six more narcos around the helicopter. I used a sync shot to take them out.
This combination scope is for assault rifles, and offers 1.0x – 3.0x zoom the same as the RUS Red Dot & G33 (found in Media Luna) and Micro T-1 & G33 (found in Koani). This is my least favourite of those scopes as the EXPS3 sight blocks a lot of view, but as they all perform the same you may want to try those others out as well if you garner for the versatility of a combined scope and red dot sight.
Just remember to switch before or during a gun fight, otherwise you may as well fit just a red dot or scope and save some handling points.