Quiltmaker,
thank you for your tipps and your offer! I live about 750 km north from Würzburg and Stuttgart in Schleswig-Holstein and as far as I know there are no bases nearby anymore.
I have already had contact to a quilting group near Stuttgart several weeks ago, they were very interested - but I haven't heard anything since then. I think I will write an e-mail to hear what is going on.
Yesterday I met a quilter from Memmingen which is in the South of Germany. She told me she knows about several quilting groups in her area but the members all sew and quilt by machine and she is only one handquilter there. You see, it is not so easy! But I won't give up.