I don’t think you can ever go in search of a Mentor.
You might read about someone and decide that they are like you, but you won’t know until you sit down and talk with them. Because they are famous does not mean that the two of you will click immediately.
I think it happens organically, over time, through successes and failures, and in some instances, you won’t even realize it until it’s over.
It might be days, weeks, or years until you realize what a great mentor they were to you without even having entered into that formal engagement of working with them.
That’s what great mentors do, they help us, without us even knowing it.