I have the 30th Anniversary CD (perhaps I should have made that clearer, but I'd forgotten its official title), which has, like you said, MB, the orchestral version. It's not bad, but I'd really like to hear the piano-only version that's heard on PT so much.
I've looked on Amazon for the MPI Dark Shadows CDs, but they must be extremely rare: only volumes three and four show up on the American site (volume two is on Amazon.co.uk), but four is currently unavailable and three is rather expensive (over $20, I believe, which is more than I'd like to spend). I've added four to my wishlist, and I hope a copy pops up soon.
Oh, and the music on DS really does make the show: every time I see Liz walk in a room, for example, my mind immediately starts humming the "Joan Bennett theme."