Train from Oslo to Alesund

Arrgh! I've been waiting to buy this ticket - following info that tix are available 115 days before travel - only to find out that the route is sold out every day of our trip! Suggestions? There are traveling, so I think that snagging a cancellation will be hard. Bus - takes 12 hours with 39 stops in the day, 6+ hours with the red-eye? Drive? Ideas? Same problem going bak to Oslo.