Ah! I think I’ve discovered it… the Holy Grail of people on Google+. Try searching by city, profession or interest: http://www.findpeopleonplus.com
If you want a little giggle, see my original rant on searching for People/things on G+ here: https://plus.google.com/108152252385291870699/posts/PwSviTjvcEu
Enjoy 🙂