The url is lesmotocyclettes.free.fr
In late 2018 the front page read:
"LE SITE EST DÉFINITIVEMENT FERME"
("The Site is Definitively Closed")
That message has been removed, and the page was updated in Jan 2020.
Hundreds of French motorcycle marques were referenced, many with fine historical photographs and correspondence with relatives and owners of the brands. For instance Elan by Sarrus had documentation dating back to 1901.
Portions of the site are available at the internet archive:
Many of the entries refer to 1000 & 1 Motos Francais by Jean-Yves Fenautrigues. The book appears to be out of print, and is not listed on the author's site at http://j-yfenautrigues.wixsite.com/motoportrait-j-y