English language Rolf Kauka site
Rolf Kauka comics and animation
Rolf Kauka book at Alibris with search box to look for others.
U Mich microfilm index indicates they have some Fix and Foxi stuff archived - as a last resort.

Usually you can hit Amazon.com and Barnes.com (bn.com) for just about anything, but Barnes comes up empty and Amazon/Borders shows one Rolf Kauka book - out of print. Both of these have search engines that can try and locate "rare" stuff, so you might still come up with something if you poke around.

Most likely place to find more would be at one of the "FanZine" sites at the top.

John