Unless you absolutely have to have this specific box set, odds are the individual French THX discs are from the same masters.
http://cgi.ebay.com/LASERDISC-LD-CDV-STAR-WAR-GUERRE-DES-ETOILES-/140463525057?pt=FR_SK_DVD_Laserdisc&hash=item20b4474cc1
http://cgi.ebay.com/LASERDISC-LD-CDV-STAR-WARS-EMPIRE-CONTRE-ATTAQU-/140463525119?pt=FR_SK_DVD_Laserdisc&hash=item20b4474cff
http://cgi.ebay.com/LASERDISC-LD-CDV-STAR-WARS-LE-RETOUR-DU-JEDI-/130441774429?pt=FR_SK_DVD_Laserdisc&hash=item1e5eef855d