ALUMNI ORGANIZATIONS. Join any these for which you qualify. Read their publications and take note of who has been promoted to which position. Use this information to your advantage by sending them a letter of congratulations. This often will get you a warm reply and a warm welcome if you later call them. Also attend alumni functions and mingle with the others in attendance. The connections you can make often will be amazing.
SCHOOL. Going back to school at least part-time is a good way to meet people with similar interests and ideas. Try to talk to each person in your classes, as well as the teachers, to find out who is worth adding to your network.