In 2016 at La Rochelle, the administrative committee of MFPP decided to make available to its members the out of print copies of “Le Pli” numerically (namely, PDFs).
This operation takes some time, but some magazines are readily available:

We hope that you will have a pleasant reading of those old publications which show that some topics are still up-to-date and that provide great details on the past.

The other issues that are still available can be ordered for 2.50 € each, or 100.00 € for a batch of (approximatively) 50 copies.