sources.list:

deb http://debian.stbuehler.de/debian/ stbuehler main
deb-src http://debian.stbuehler.de/debian/ stbuehler main


gpg key:

gpg --keyserver pgp.surfnet.nl --recv 80121CD2479689D8

and (if you are root):
gpg -armor --export 80121CD2479689D8 | apt-key add -

or as user:
gpg -armor --export 80121CD2479689D8 | sudo apt-key add -