You could start by looking in German folk - tale collections. Some old and comprehensive books might contain such an unusual story. Libraries with a good collection of German literature, especially those focusing on folklore, would be a good place to start.
Try searching in specialized German folklore databases or websites. There are many platforms dedicated to preserving and sharing different cultural stories. You might also ask German scholars or enthusiasts of German literature and folklore, as they may be aware of such an odd - sounding story.