How can a distance education student get a copy of the lecture notes? I am a distance education student at a Parisian university, and I am currently preparing for the exam in a research-level mathematics course.

While on-campus students have attended the lectures and presentations of sample problem solutions, distance education students only get incomplete lecture notes in pdf format, sample problems without solutions, and a list of recommended textbooks.

I think I was quite successful studying about 85% of the course this way, but the last one or two lectures and sample problem solutions cover some very advanced material, which is not adequately addressed by the recommended textbooks. I also could not find this material is a sufficiently concentrated form in research articles, and I estimate that it may take thorough reading and understanding of no less than 50 articles and maybe 3 months to properly figure this out by myself.

One of the professors recommended to me that I get a copy of the lecture notes and sample problem solutions from a student that attended the course in person, but when I requested a few email addresses from the secretary, she said she is not authorized to divulge that information. I asked the other professor of this course, but got no reply.
I can't go to a course lecture to locate such students, because the last lecture was some time ago.

I would like some advice on what else to try to obtain the lecture notes.
Some comments and the already given answer give advices that can be counter-productive in France. You mention that this is about a research level course so I understand that this is a "Master 2 recherche" course.

It is unlikely, for privacy reasons, that someone will give you email addresses of other students. My advice is to ask the professor to forward to a few targeted students your request.

Going to the department chair/dean will probably be useless. If you really want to go up the ladder, ask to the person in charge of the master 2. But it will probably be useless too since in the French system professors are free to do as they want for their lectures. For those surprised by that last sentence, keep in mind that having lecture notes in pdf and a list of recommended textbooks is something that you don't have in all lectures in France.