Have you tried...
P&O Ferries - http://www.poferries.com/tourist/
Sea France - http://www.seafrance.com/seafrance/opencms/uk/en/passenger/index.html
Speed Ferries (to Boulogne, near enough) - http://www.speedferries.com/
and then there's the channel tunnel...
http://www.eurotunnel.com/
although the tunnel website seems to be down at the moment.