Sorry, there's no register or directory of email addresses. Your only chance of finding the address you want is to contact someone else who knows it and ask them to pass it on to you.
(OK, there's also a very small chance that googling the person's name, and possibly their interests, could find their email address. I once helped someone contact an old friend in New Zealand because I knew that they were breeders of English Setters and a Google search found that they were the Secretary of a local dog club. However such occurrences are very rare).