Well, English RT scripts may be plentiful and possibly even fairly easy to whip up yourself, or to have the students write, but French ones are a little scarcer... dramatic pause... but they DO exist!
5 sources of RT FSL scripts
Cheneliere has a kit that you can buy. A little pricey as an option if you're just looking to pull something out in an emergency or for a couple of days. Pros though...it's a traditional publisher and your school or board might be more willing to dish out the money for that than for individual teacher-created resources. They also come with some activities and rubrics (although I don't believe either have been or will be updated any time soon to match the 2013 Ontario French curriculum expectations.)
Ms Joanne is a French Immersion teacher in B.C. who has placed a whack of RT scripts, mostly based on the classic fairy tales, on TPT. She sells a bundle for $16 or you can buy them individually. Check out her free version of Blanche Neige to give you an idea of whether it'll work for your students.
Scruffy Plume has had a recent update to their website. This site has been around a good long time, but the appearance and navigation was a little hard to bear. They've jazzed up their site a lot recently, and it's still a work in progress. They've got scripts for Greek myths in French, aboriginal tales, and several other appealing options. The accompanying grammar sheets may not get as much use today as they would have in the past, but really, the play's the thing, right? ;-)
TFO has a bunch of texts for what they call "Lecture en spectacle" available for free download, for educational use. Not all are RT scripts, but if you comb through the grade level tabs, some named "Conte à lire" are (Le chef et le charpentier, for example). I'd say almost no text beyond the grade 2 level are for Core French, on this site, but many could be used in different ways in immersion classes. Or maybe high school Core French.
And of course, there's AIM as an option, which I didn't include in my "top 5" because I feel like the plays/scripts are either something you legitimately have access to and use, or you don't. No one is about to go out and purchase an AIM kit just to do a Reader's Theatre activity in their classroom. But keep it in mind if you have colleagues that use the accelerated integrated method but you yourself don't.
If there's a good source that I've overlooked, please let me know in the comments below!
Updated to add...
Huit petits théâtres de lecture (Saynètes inspirées de contes traditionnels)
Check out a video of some little francophones reading one of the scripts in this publication, which looks like another great option!