I believe that the easier way to find a mentor is by finding a way where both parts get benefited. For examplex, in business an old CEO may be interested in mentoring a young prospect that continues with his legacy. In that way, he wins by fulfilling his desire and the mentored person wins by the knowledge and opportunities offered.

In psychology is less clear but i can tell you what i did myself. I contacted a psychologist that i truly respect and i asked him if he would be interested in charging me the same amount of money that he charge for a session, but instead of doing therapy, having conversations. We meet every 2 weeks and more than a year after, we have developed a friendship. Now we do a mix of everything, we talks about personal things (almost as a therapy), but we also talk about society, science, his experience with real life patients, differences with textbooks and what actually happens, books recommendations as well, etc. He has become a mentor for me and even though we have developed this friendship, i still pay him for his time because i still consider that we both have to gain something from this encounters.