Searching for a stage or internship is one of the most difficult things in student life, especially for master students. Here are the list of best websites that can help you to search an ideal stage:

https://www.1jeune1solution.gouv.fr/stages

https://www.cidj.com/emploi-jobs-stages

https://www.letudiant.fr/jobsstages/conseils-stages.html

https://www.directetudiant.com/theme/offres-stage.html

Good luck