I am sure you will find many execs willing to mentor. Are there specific disciplines/industry/company size you are interested in?
I learned invaluable lessons interviewing execs day in and day out during my time as an exec recruiter and will continue as well as being a mentor myself. Having and being a mentor is huge for any career and life. Good for you - I will contact you directly with referrals.
Also, you may try to post this question on
LinkedIn Answers > mentoring because you have a lot of contacts and will get a large reply. I would be more specific to get targeted leads here and there.