The document is referenced on the last page of a just-released unredacted CIA chronology of Mexico City. See the last page. That comment can be more conveniently seen in of the searchable copies released earlier.
Note written by COS: This guy GARRISON is so far gone that would not be acceptable in any luny [sic] bin!!
"COS" evidently refers to the Chief of Station in Mexico City. The Chief of Station of Mexico City at that time was Win Scott.
Previous Relevant Blog Posts about Garrison's Interview in Playboy
Eric Norden, the journalist who interviewed Garrison, wrote a memo to Playboy Magazine with information from Garrison that could not be printed
Garrison also wrote a memo to Playboy with additional information and Norden wrote a second memo with secret information.
Garrison lied in his Playboy interview about lie detector tests given Perry Russo and Vernon Bundy.
Garrison mangles the story of Rose Cherami in Playboy