From the Out of Left Field department, a label called Atlas Réalisations will be releasing a CD of works from George Martin, including a new recording of an un-recorded score to the Joffe film (which reports say he was originally hired to score).
EDIT: From a blurb at a premiere where he had various pieces of his work played:
" “The Mission Chorales” was part of a score he wrote for Roland Joffe’s 1986 film “The Mission.” The score at that time was only a 30 second fragment, Sir George explained. He was replaced by Ennio Morricone for the soundtrack duties after a producer shake-up, and the score remained unfinished until Mr. Firestone expressed interest"