Cable TV channel "Chiller" is running several Dark Shadows marathonsin the near future, including a 24 hour one beginning March 29th, 2009 at 6:00AM ET and running through March 30th, 2009 5:00AM ET. They are showing the complete first season and then will repeat episodes One through Ten immeditately afterwards.

According to the schedule, they have additional marathons planned:

April 26th, 2009 9:00AM-4:00PM ET: Episodes One through Eight
April 27th, 2009 2:00AM-5:00AM ET: Episodes One through Four

Check the Chiller TV schedule for broadcast times in your area:
http://www.chillertv.com/app/Schedule/