Find them and ask them. Be sincere, and interesting. Pick specific people, study them, and have specific reasons you want to talk to them. Write a short, coherent letter and if your motives are compelling you may get a few bites. Don't be stupid and sabotage yourself by sending a boilerplate research recruitment letter to Warren Buffett or someone.
Recruiting is always hard. Even when I do AdWords or something, I still have to harass my survey respondents for weeks to get the interviews lined up. And even then, it's rarely more than 50-80% who show up for their scheduled, paid interview.
Also - C-suite folks generally don't mess around. Be prepared to make good use of their time or they'll be bored in 15 seconds and probably bail on the interview. You better know what you're doing as an interviewer.