I don’t know about a 35mm scan of Song of the South, only a 16mm scan available on myspleen.
This is one of the releases on myspleen:
V2 Disney’s Song Of The South [35mm Restoration]
Song Of The South is well known as the “Banned” Disney Movie, with no official DVD or Blu-ray of any type, with the highest quality official version being a Japanese Laserdisk. This is based off of a 1080p 35mm scan, this is a huge improvement over most versions.