There a number of services for finding email addresses. If you know the name of the organisation an individual works for, you may be better trying the WWW site of that organisation. General search engines such as Alta Vista can also be used to search for addresses.
Directories include:
(a) Bigfoot: addresses taken from many sources. http://www.bigfoot.com
(b) Four11 Internet White Pages: also includes a database of USA telephone numbers http://www.four11.com
(c) X.500 directories: listing of email addresses at sites operating x.500 software
(d) Finding E-Mail Addresses of Individuals: comprehensive site giving varied search information and links divided into areas including searching specific institutions, subject-specific areas, discussion lists , Usenet groups, as well as links to general sites to search. http://www.ex.ac.uk/~RDavies/lib/address.html
(e) Netfind email address directory, mostly academic organisations: http://info.lut.ac.uk/dir/netfind.html