There's an appearance mod that seems to only be available on low-level (ie; blue) vests that has no front armor, so you can see the shirt/jacket etc underneath.
As it's only available on blue vests, the odds of you getting it at level 40 are pretty close to zero. So you need to match make with someone with a low-level agent and ask them to share the vest with you if they get it. Of course you could use a new agent if you have a free slot. I do not.
It's a Sokolov vest, and I got it from playing with a level 14 agent (not SHD level 14). In fact, I had two other guys from our clan join me and we had the lower-level guy drop his green/blue/purple non-gun loot, one guy picked it up, dropped it again, my other mate picked it up and then dropped it from me. This way we all got any mods. After about an hour or so, we had about 30 new appearance mods!
Because there is targeted loot even at lower levels, you could farm Sokolov.
Below is a couple of pics of what the result is.