i found a cd at of all places a japanese record store called "the original music from dark shadows deluxe edition". ... i have no idea where else this cd is available.
It's still available for order on most popular Web sites. And BTW, the CD was a reissue of the soundtrack that was originally released in 1969, but with the addition of the two Ron Barry interview tracks.
As for my favorite DS music, I love it all. But if I had to pick one track from the TV series, I think it would be The Hand of Count Petofi, a reworking of which was used in both hoDS and Nods (and it's called Banabas and Carolyn on the movies CD). Something about it is just so evocative, mysterious, and, dare I say, subtle, which isn't something one can say of all the pieces that were used on the show.
However, as a whole I think I enjoy the music used in NoDS the most. Whenever I'm in the mood to play one of the DS CDs, I always seem to go to that portion of the movies CD first. And within the film itself, it seems as if every piece fits with the goings on so perfectly.