Welcome in Vienna!
I happen to know two excellent luthiers (violins), but I am not sure, if they do guitars as well (and I don't know if they speak English)
Gerlinde Reutterer, Mollardgasse 85, 6.Bezirk
Roland Schueler, Viktorgasse 12, 4.Bezirk
Hope they can help you!
Enjoy your stay in Austria