The README states the source came from https://github.com/historicalsource/defender. "A collection of historical source files, for education and perusal." Which begs the question, where did Historical Source get it? Alas, there is no indication.
http://archives.museumofplay.org/repositories/3/resources/22...
So perhaps it was scanned and distributed from there? Seems unlikely since the code was either printed on paper or stored on old 8" floppies from the development system. But you never know.
EDIT: looking at Historical Source's repo, they have a LOT of old Williams IP here. This was copied from someone's development machine somewhere.