1. Contact the university where the person got his Ph.D. Maybe they'll have his or her whereabouts.
2. If the person is still pursuing a career in the academic setting, he or she might have published something else other than his or her Ph.D. dissertation. Go to ProQuest and use his or her name as your search word to see what comes up.
3. Contact U.M.I. Dissertation Services (Bell & Howell Company) which has a dissertation abstract database for people to access almost every doctoral dissertation accepted in North America since 1861. But it has been a while since I used their service ...