This achievement will require some saving money before you can do it.
Argo can be located at Base Station which is left as you come out of your house. Just go around the stairs and your see Argo in front of you a little way ahead.
Argo had only two pieces of intel to sell to me. Which was...
Handgun Weapon Arts - 450,000 C
Shotgun Weapon Arts - 350,000 C
Buying either of those should unlock your achievement.