I agree with 1WildR/T that the Right Stuff parts may be exactly what you already have since they have the slider brackets pictured and you need the pin style. There are millions more of the '76+ disc brake parts than there are of the 70-71 style, so they are a popular swap.
I'm afraid you are going to have to bypass the big parts suppliers to acquire these parts and deal with small shops or individuals. Tony's Part, a site supporter, may be able to help you. However, I don't recall his username here. Perhaps someone else can jump in with contact info.
It certainly would be simpler to purchase 72-76 rotors and pads and ship them to France and replace and get the car back on the road. You could then sell the 70-71 disc and pads to someone else in France or elsewhere on the continent and avoid the shipping charges back to the US. But that won't solve the owners desire to have the correct year parts for his vehicle.
