I am mentoring two guys myself and know a couple of friends who also have their mentees. If you are determined, you can achieve it by cold emailing people (this is how I got my mentees). Find a person, which has some skills or achievements that interests you (eg. he/she is a startup founder) and ideally you have something in common with them (eg. alma-mater, hometown, nationality, niche hobby etc.).

Then simply reach out on linked-in, introduce yourself, expand on something which you have in common to establish some familiarity and clearly state that you would be interested in some advice/mentoring to achieve your goals. You will likely get a reply that your mentor is too busy for this, but maybe he/she can spare an hour every other month, which would already be plenty and super useful.