I have described the Backwards Method in the previous post. To summarize:
Step 1 – collect as many email addresses as possible from pages that may contain relevant ones. Get emails from Google results, pages containing contact lists, anything remotely promising. But probably keep your searches returning only results from the past 2-3 years since both emails and careers get changed fast.
You can get quite creative in Googling. Don’t forget to dig deeper into sites that promise more content judging on snippets.
It is not a problem even if your collection has 98% emails that are “wrong”.