Brad Parker recently announced:
After a long and interesting search I uncovered a set of 9-track tapes which appear to be a snapshot of the MIT CADR Lisp machine source code from around 1980. This is not the final source code and not the last source release I will make. It is, however, the first source release.
Tom Knight and others at MIT helped me secure permission from MIT’s Patent office to release the software. I am indebted to him and the others for making this possible.
Follow the link above for a compressed tar file containing the tape images, extracted files, and extraction software, plus MIT’s license, a README, and a link to Brad’s CADR emulator.
(Via Bill Clementson via Lemonodor; see also Bill Hyde.)
I’ve added a link to Brad’s web page in the Zetalisp for Lisp Machines section of the History of LISP website at the Computer History Museum.