Here are some French sites: (English versions available)

Fine Resophonic, resonators
http://www.fineresophonic.fr.st

Alain Quéguiner, acoustic guitars maker
http://www.queguiner.fr.st

DNG, Guitars and basses
http://www.dng.fr.st

WHAT IS A DOBRO/RESOPHONIC GUITAR?

A resophonic guitar, as they are now called (by those who do not want to get in trouble with Gibson's legal department, who now own the copyright to the name "dobro" and "Dobro"), is a type of guitar played horizontally. The guitar is fretted with a steel bar (the "steel") in the players left hand, and the strings are usually plucked using fingerpicks on the right hand.

Read more: http://www.guitarsite.com/newsletters/990719/8.shtml?nl61

National Reso-Phonic Guitars
http://www.guitarsite.com/database/Makers/rec/774/?nl61
Metal body resonator guitars played by the world's great blues artists since 1928... .....These instruments were first created in the era of the Hawaiian and Jazz Bands, prior to electrical amplification. All sorts of musicians, Hawaiian, jazz and blues, wanted louder guitars: to be able to be heard alongside horns; to project out into music halls or smokey night clubs; or, to be the loudest guitar on the street corner. In response to this need, the mechanically amplified resonator guitar was created.