You're not going to like this answer but I assure you that it's written solely with a view to accuracy, not with any 'nastiness' intended:
Firstly, nobody is ever required to provide a reference for anyone else. When an employee has been dismissed, the former employer will usually simply refuse to provide any reference. (That may well be what's happened here. i.e. your friend's son might be getting turned down for jobs simply because a reference is being refused, rather than through the content of any reference which has been given).
Secondly, anyone is free to write what they like, about who they like (or dislike) and send it to anyone they choose to (whether asked to or not) as long as what they write is either;
(a) factual ; or
(b) "fair comment".
In practice, your friend's son might have to seek employment (in an alternative field) where references aren't required. He could then later seek to return to his former occupation, providing the name of his most recent employer as his first reference and, perhaps, getting a reference from someone who knew him during his training to provide a reference relative to the field which he was seeking to re-enter.
Chris