You have weak search skills ;)
Anyway, there is no such thing in Castle Ravenloft, but Wrath of Ashardalon
comes with Campaign rules according to the box. That being said, there's nothing to stop you from playing through several campaigns. It might be a little unbalanced to keep equipment/levels, but if you only have 2 healing surges total for the entire "campaign" that should balance it out I guess. Maybe a bit too much. So might need something like "regain 1 healing surge between adventures if you have less than 2".