Metropolis Police Stations (I think all of them). The recruiter will pop up outside of the station in a Green Lantern uniform. I'm not sure when exactly he pops up, but when it says 5 minutes until ring war event, he'll definitely already be there. The quest is called Fear VS Will.
ah, fear vs will. I played that but didnt know it was the ring war event. I still have it in my quest log. I ended up quitting the event because there were three heros along with me and probably a dozen villians in the area. The villians just camped at the hero respawn area, which was not inside one of those protective bubbles, and ganked us every time we respawned.