Cant find blue shield guy

I have a really good weapon that I really don't want to lose or throw away. It's the best weapon I have had, but I can't repair it anymore. So I searched up how to repair and found out about blue shield guys, I have only seen one in the entire game and I failed that mission. I have been looking for them for 3 days IRL. I only know 2 locations: One is at the north of Slums right next to a safe zone, the other is on a train track. I run around looking for them the whole 24 hours in game AND I STILL CANT FIND THEM

Edit: Thanks I realized what I was doing wrong, I was playing co-op the whole time.
This guide worked: https://steamcommunity.com/sharedfiles/filedetails/?id=748947354