Jack King-Spooner's part of the OST (which includes the much-lauded prologue song) can be purchased directly from him here: https://jackking-spooner.bandcamp.com/album/an-outcry-an-soundtrack
All proceeds from that part of the OST go directly to him.
It includes a few tracks that aren't in the game yet.
Otherwise, the full OST will not be publicly released until the game is complete.