Tokyo is a great city, but there are so many (thousands) of places to list where expats meet up that it's nearly impossible to list even a few. Even if someone listed one, it would be impossible to give a proper address or directions, and I can't really can't describe why. My advice is to wander the city around his residence, as undoubtedly there are numerous places nearby, especially in Roppongi. The first place that comes to mind is the Beatles bar, where every night there is a live Beatles performance. Tons of expats there. Have him ask around - nearly everyone knows where that is.