Here is a massive database of Google+ shared circles. It’s in the form of a google document and broken out by interest area.
Reshared post from +Laurence Hubbard
Looking for a particular circle?
Here is a database that lists shared circles of many types.
Socializing with people who have a common interest is one of the top reasons why people use social networks.
So check the link and make some new friends!
Google+: View post on Google+