1. Use Google for "Name Surname" and "gmail", look thru first 2-4 search results pages
2.Use Google for "Name Surname" and "pdf" - often in pdf there are contacts of the author
3. Install Chrome extension "Connect6"
5. Check for personal blogs and sites: sometimes there are contacts available.
6. If the person has personal web-site check the registrant information (use whois services).
7. Install Chrome extension Rapportive to check emails you found are valid or not. Click in Gmail "New Letter" button, put email that you found or imagined and it will show you the connection in LinkedIn if the address was registered in LinkedIn.
Of course, then warm introduction is always better than a cold letter.