Post war German glass is sadly underappreciated, that's why information is sparse. There aren't any decent overview type books on modern German glass as well. To be honest, I'm already very happy if I manage to find both the glashütte and the designer of a piece...
Just a tip: an interesting link for German glass is that the city of Düsseldorf has put all their culture objects in a database online. Since they also have the Hentrich glassmuseum somewhere, their database contains as of today 2642 glass or glassmuseum related objects. If you go to the left, you can select 'suche' under 'd:kult' to find out if they have more objects of a particular designer or glashütte. The glassmuseum has a large amount of Wiesenthalhütte glass (apparently they acquired a collection from designer Klaus Breit, who designed for Wiesenthalhütte), and they also acquired lots of Dutch glass from Leerdam and Maastricht at some point.
If you search for Gangkofner for instance in the search program, you can see some of the other objects he designed.
Astrid