If DC ever does a Showcase Presents: Shazam! Vol. 2 the two Adventure Comics stories could appear therein (I think they would just fit in there), but I wouldn't hold my breath, it's been exactly three years since the first and only volume so far.

That's if you like b&w telephone books, but it's difficult for me to see where else they're going to reprint them, unfortunately.

I love Don Newton's art too, and I don't understand why somebody (such as Dark Horse - they've published comics with greatly inferior art in hardcovers) hasn't reprinted his Phantom comics in color hardcovers.