All maps of France can be obtained easy and very reasonable priced at the website of the publisher IGN http://www.ign.fr/, click on 'boutique loisirs'.
They have all the maps of France on three scales:
TOP 100 = 1:100.000
série orange = 1:50.000
série bleue = 1:25.000
All GR's are on the maps, we walked with the TOP 100 maps through France and that was very doable.