I’m not really sure how to join a CSA in Germany but I know you can because CSAs originated in Germany in the 1960’s. According to Wikipedia, the term for CSA in German is Landwirtschaftsgemeinschaftshof (oder auch Gemeinschaftshof).
I did find this link about subscription based farming in Germany and this blog post about an American couple joining a CSA in Switzerland. I know it’s not the same country but maybe you can email them to see how they found their farm?
Any other tips out there?
Thanks for reading!