Suggest determining what you need, why THEY would want to engage with you and be clear with yourself and them about the relationship expectations. Your needs will likely be filled by one or more people with skills and interest in you and/or what you're doing. Here is a way to look at it:
Adviser - Someone who shares knowledge in an area you're less competent
Mentor - Someone who is committed to you and your development
Business Partner - Someone who shares your commitment to the enterprise
You'll notice that as you go down the list, each has an increasing level of skin in the game.
Advisers are everywhere, from angel groups, industry groups, places like here, surfing Linkedin. These relationships are usually transactional in nature though they may include many transactions over an extended period (including participating in an advisory board).
Mentors are a deeper relationship. It is more about you and your journey, though a mentor most likely has experience in areas you'd like to acquire. Since mentors aren't one size fits all, the best ones come through people you know or people who know you, though you can use the channels above to find one. Since you're asking for someone to invest time and energy in you and your development, be sure they're interested and are willing to make the time commitment. An adviser might be willing to become a mentor.
Business Partners are another thing entirely. Key to a successful partnership is to first know yourself, the skills you possess the type of relationship you're looking for (peers, hierarchical, co-investment..etc) and let your network know what you're looking for. Local entrepreneurship networks, colleges, friends, angels can be good sources depending on the business stage. A skills fit is important but make sure your personalities work together. This is a marriage.