Since the start of the real estate collapse, the notaries, who are the real holder of the real estate prices because every single transaction goes through them, conveniently stopped publishing prices.
Notaries are like the land registry office of the UK, where you can find about the real sale prices instead of just using the asking prices of the ads.
One cannot buy a house in France without going through them.
But hey, it's communist France, and Notaries are doing whatever pleases them. Why shouldn't they anyway? They have a state monopoly, so it's their legal right to use it (and abuse it).
Last time they published anything was in May 2009 but as you can see, they stopped publishing the monthly data way back, in July 2008, which I believe was just after the peak.
Let's hope they prove me wrong though and publish fresh and recent data shortly.
Real estate stats (main page):