The best way to find a mentor is to look around in your industry and see who you feel has accomplished what you're setting out to do, and that you gel with the way they did it (values, brand, etc).
"Ask for money, get advice. Ask for advice, get money twice"
If you can get a warm introduction, do that. If not, you can always cold email them with a specific issue that you want advice on .. ideally it's something super relevant to their life experience and interesting enough to get their attention.
Never ask them to be a mentor. Mentorship usually develops over a couple meetings and is informal.
The value to them is to give back to the next generation. As long as you listen, execute on their advice / or not, AND follow up - then they'll continue to give you some time.
Mentors are best for those large life decisions that most people turn to their parents too ... those decisions are interesting for most noteable people to give you 15 minutes on a call to discuss.
You might already have a mentor and not realize it.
Depending on where you are in your career and who has given you advice in the past or been a sounding board...that could be a mentor.
In my career I have had mentors that were bosses and not until after I left those organizations and maintained those relationships did I ever really call them or see them as a mentor.
Look back in your career and see who did that for you and that might be the best place to start.
I have had lots of mentors and I've never asked.
The value a mentor gets is a good feeling that they are creating impact by spending time with you.
You give them this feeling by actually DOING the stuff they advise you to do or help you to see.
It's not often that someone actually takes advice and runs with it and comes back to say "Thanks, I did it. It gave me this result. Now I have another question..."
Forget strategy. Simple principles are all you need.