1. Do stuff: Pick up projects. Do open source work. Volunteer.
2. Network: Meet people in person.
"Finding a mentor" is a misnomer. You don't "find" a mentor any more than you find a girlfriend or spouse. A relationship with someone who can mentor you is the byproduct of everything else you do. Get out there and get busy. You may be surprised at the people who take an interest in you and your work.