Not quite as many as some people, but Ireland is full of these events. Everybody knows everybody, somehow. Most of mine involve bumping into people in London in various places, but the greatest one of late:
Brother-in-law recently moved to MEL and was telling me about his friend there who grew up at the same time, in the same small-ish town in Poland (~50,000 people), yet the two of them had never met until they moved to MEL. Apparently there were two high schools in town and they went to different ones, yet they had common friends.