Where can I find the G-man?

For those of you who are unaware, the g-man is a guy in a suit with a briefcase, with really creepy green eyes, who can be found following you EVERYWHERE in half life the original. in half life two I KNOW he is also stalking you because that is most deffinantly his occupation. (professional stalker alert) I have encountered him following me only twice through the entierty of the game half life two and the episodes, and to be more precise the only time I ever spotted him was in episode two. The first location was after you rescue Alyx from nearly dying you go to a bridge and if you get there quickly enough, on the bridge he is walking there. the second location was in White Forest in the room where there are 9 tv screens and only 8 are working if you watch the screen long enough he appears through the static. I suppose now I should get to my question. does anyone know if he can be found in more places and if so where can I find him?