One option is to stick around this site, there are questions that I have and I am sure others have benefited greatly from the answers. Questions that I would have not thought of. I am not talking about the technical support how to type questions but the questions regarding being a professional graphic designer.
Some examples:
How to handle client requests to violate copyrights?
What are best practices for choosing and pairing fonts?
How do you deal with clients who bash your designs?
There is a plethora of high quality content on this site that will give you personal first hand answers from designers around the world.
Another idea would be to try getting an internship.
I believe this would be the closest way to finding a mentor. I have not personally met a graphic designer that had a "mentor". The designers I knew did an internship while in or after college.
The internet is primarily how you will find these positions but I however got some great advice from a local marketing agency. While I was looking for an internship during college I went to a business district in my town. All I had was a black portfolio and a resume (not even a website). I walked into the place and asked if they had any openings for an internship.
They politely said no, but after I left I got a call about 10 minutes later. He said that he liked my enthusiasm and initiative to walk into a place that he wanted to review my portfolio and take me on a tour of his facility. He talked about the type of clients they get and the work that they do in-house and how they do it (The how to was more for their photography studio).
So my advice is to keep working, practicing and participating in online forums. With the growing web, it is easier to find information on graphic design and get opinions from people all over the world. Whether you participate in the Graphic Design Stack or another online community, you will find people who are willing to help.