You can often find torrents around for sacd's or dvdaudio - but there isn't any good place as far as I know
Not to mention a LOT of surround music is mixed terribly, with the exception of a few individuals. Steven wilson does amazing surround mixes, and has remixed several commercial releases
The quadraphonic mix of Dark Side of the Moon is one of the best multichannel compositions in existence.
Problem isn't the MIX, but the way the musicians intended to display the composition.
The quadraphonic mix of Black Sabbaths Paranoid album sucks big time (but is also funny as hell).
The new The Cure album is well done in Dolby Atmos, but not really my taste in music.
Spatial Audio is one of the terms used for anything with height information: Binaural and Ambisonics (although these two don't always feature height), Dolby Atmos, Auro3D, MPEG-H or some experimental other formats.
Other terms that mean the same thing: 3D Audio, Immersive Audio, Surround+Height
Not sure is helpful, but albums made with Q-sound gives excellent (engineered) soundstage width. Try Roger Waters album Amused to Death, or other albums made with Q-sound.