I have to correct myself.
My brakes pads are probably original "short".
My brakes seems to be exactly the same as these ones , and I probably could mount Mafac replacement pads (I would have to cut them to fit the length)
Mafac S
That said my initial question remains , any good replacement "modern" pad for that.
Velosepia: Vintage Mafac « S » front & rear brake set