Nope, there are emails circulating and you need to have connections to find out about that. A bit unfair, but that's the way it is. This week I got 2 ads of units searching for stagiaires atypiques, however I'm not very interested.
I guess if you're not on the mailing lists the best you can do is to contact the heads of units and ask them whether they would accept you.
Many trainees continue working at the Commission as stagiaires atypiques after their stage.
If you don't know what it is: stage atypique = unpaid
