The Bavarian Academy of Sciences is developing a database of medieval German sources from 750 until 1519. It already includes c. 5.500 sources in Latin and German. The source for this database is Repertorium Fontium Historiae Medii Aevi that was printed in 11 volumes between 1962 and 2007.
Is it Viking Age proof? Yes, absolutely – take for example the text Ludwigslied that describes the victory of the Franks over the Vikings. Also mentioned are Thietmar of Merseburg and Adam of Bremen.
The site is in the German language, but Google Translate or a little familiarity with authors and texts should help you out.
Visit site: Geschichtsquellen des deutschen Mittelalters.