The Russian Red Dot is described as:
A Russian-made red dot scope. Swap reticles while aiming.
It can be found in north-eastern Villa Verde, inside a cartel network station side mission building. The accessory case is on a desk on the top floor of the building on the east side.
You’ll have to at least breach the doors to the network station with explosives to get inside, whether you attempt the side mission or not, but I have a separate guide for these which makes them easy!
Beware that to the west on the opposite side of the road are a handful of cartel which will come your way when they hear the commotion, so you may want to deal with them pre-emptively first.
This scope has a 1.0x zoom and a choice of two reticles; a chevron or three ticks in a T shape. It’s quite a bulky red dot, but is clear while aiming. Worth giving a try on your SMG load out at least.