Music discs that included midi remixes of "As time prevails" and "Sally Sparrow" was added in 1.16.5, but were never given a way to be obtained within survival...
This should be rectified using Global Loot Modifiers in order to make these discs spawn within vanilla chests.

Since we are now on 1.18.2, this leaves a lot of backporting than would really be less than desired, as the obtainability of these discs has been left out of every version since due to directly porting up source code

Fixed for 1.16: aabb40b
Fixed for 1.18.2: e1af768