ADAC, the German Automobile Association.
They sell Green Card Insurance (third party liability insurance only) on a monthly basis for foreign registered vehicles. Mr Jens Messerschmidt ADAC RVE Am Westpark-8 81373 Muenchen Tel.:+49 89 7676 2266
E-mail Jens at jens...@zentrale.adac.de
Note: Their website is in German only. For non-German speakers, contact Jens directly, who speaks English.
"The good news is that basic third party liability green card insurance for foreign registered motorcycles (called Grenzversicherung) is available through ADAC for 22 Euros a month. The bad news is that it is not available by post or email. You must show up in person or assign someone to go to an ADAC office with your original registration paperwork to apply and pay for it. This from Jens Messerschmidt at ADAC."