My first supervisor is deceased. I'm thinking his number is unlisted.
Locating contacts (work or personal) from decades ago has proven to be near impossible in many cases. Many people have ID theft rationale for removing all traces of them off the internet and everywhere else possible. Some of the people I've known are deceased, and untrackable as well. We've lived in apartments and condos while homes were being built (and have no clue whatsoever those addresses were, as they were temporary lodging). I've also taken a couple of jobs and walked out of them on the first day (not all employers disclose THEIR negatives, but choose to let workers find out for themselves how bad the workplace or the co-workers are/is).