Next time, I would try reaching their Public Relations group for help. PR people are almost always accessible by name, phone, and email -- they're usually on the bottom of every press release that goes out. They also have good internal channels to every part of the company and know who to contact.
Googling for "american express public relations" turns up a page with three NY-based vice presidents, with direct lines and email addresses listed: http://about.americanexpress.com/news/media_contacts.aspx