Boy I gave it quite a try and they are indeed very hard to find.
If you are affiliated with a college/university -- or an institution that can make "inter-library loan"-type requests -- perhaps reach out to a librarian and see what they can do?
If not, maybe see if a public library near you can help you track it down?
Apologies if these suggestions aren't very helpful. The subject matter of these articles are definitely very far from the fields I specialize in; that being said, someone who is in that field may know where to look better than I do :-) Best of luck, I hope you will be able to track them down.
Edit: Lelong-Ferrand (1971) has an entry on WorldCat, which lists the libraries that have this article! Many libraries do provide scanning services, too. (However, gaining access to that may depend on you being affiliated with their library 🤷🏻)