I think another way to get a mentor for more general advice is to read. Some of the greatest minds in business have written books. Read their books and they can kind of be a proxy mentor via a book. I have been reading a lot of books lately and it has answered a lot of questions, and given me things to think about I have never even thought I would be thinking about.
I think you have to be doing something - or at least, trying to do something. When you hit genuine questions you need to decide, take those questions with you everywhere you go.
People who engage with the questions and seem to bring genuine experience and insight are already mentoring you - if only over coffee at some event. If they're willing to stay in touch and give you their contact details, take the next question to them (all of them!) too. Build up a relationship around this 5 minute question + answer.
Now you're getting more eyes on your issues, you're getting to know who's bringing new insights to you, they're getting to know you and maybe it's time to 'pop the question.'
One thing to bear in mind is that - in my experience - the best mentors are not pro-active with you. Does that sound strange? Think about it a bit. You need someone to nag you - but almost anyone can do that. You need to actively collaborate with some people - but that's a team relationship. The ideal mentor comes to your issue fresh - and hasn't spent a whole lot of time in between encounters thinking about what you're up to.