The
Onyx Boox M96 may techinally meet the specifications you gave (unless you consider it a tablet because it runs Android). However, I assume that you're looking for something closer in size to the Kindle.
shopereaders.com seems to still sell some presumably-out-of-production models, like the
Icarus Pocket, and they claim to offer a one-year warranty (see the end of
http://www.shopereaders.com/terms.asp). The prices are in Canadian dollars. I don't know if they ship to Germany.