Only 800 or so cars used the push button door latches. And, it is only recently that the S1 has generated interest. Every book you read will say to avoid S1s over the later cars. It was also common to toss the S1 doors and fit S2 ones for their opening windows. There also used to be tons of scrap Renaults you could source the parts from. Now they are becoming rare as well.
I found spares by searching ebay.fr using the French part names.