This is a common problem with working reports from any institution. I also have written up research in a "Working Report" series in the past. Often that report was only written for others within the research team, group or project in order to disseminate the information generated or gathered so far, or to capture the thinking done so far. Sometimes there are only a few copies produced.
Sometimes, when a more formal system is in place, copies of the report are lodged in the institute library and added to their catalogue, but sometimes not. Sometimes the reports are just added to the local library of the group. Capturing copies of such working reports was difficult even for a contemporaneous researcher and one would have to get the author to make you a copy and send it. Some of these rare copies of important reports have been cherished in the research libraries of other groups as liberated treasures. For a researcher coming many years after the event obtaining a copy is an exercise in forensics.
Today, with the advent of digital publishing, dissemination and archiving these old and obscure paper pools are being disposed of and becoming less and less accessible. The librarians see them as trash. They can see no value to an internal document that has not been consulted in 30 years and want to recover the space, often not for storage, but to "open the library for social purposes". I have witnessed huge skips of books and documents at the rear of institution libraries.
Some archivists have been aware of the problem, and I was part of a consortium that bid for funding (at national level) to attempt to recover and digitally archive works similar to this, but the accountants could see no value in it; but I digress.
It will be very difficult to locate this. Only the author would know, and they may have lost their copy. I tried to retrieve copies of some of my old reports (going back to 1974) in full text and found my own personal archives had holes in them caused by system, institution, office and continent moves.