I have worked with large companies over many years. Getting past the gate keeper is not always easy. But they all use email.
Create value for them that they can access
Publish on Linkedin Publisher, upload slide decks to slide share, create videos on linkedin. Put links to these in your email signature which they will receive when they hear from you.
When you meet them, ask face to face if you can add them to your mailing list and then set up auto responders to deliver this content to them in short simple emails with a link to the content.
Do get in touch if you would like to discuss further...
Warm regards, John