A friend who is a huge CONSTANTINE fan reported today that a DVD set of the short-lived series will finally be released. I think it is going to be a "made on demand" set which most likely means that it will be DVD-Rs rather than fully pressed discs, but there will be some extras. The only thing she mentioned specifically was a video recording of a San Diego Comic Con panel for the series.
She mentioned 13 episodes which may include ones that were not aired. If I see a link for the set, I will post it.
G.