Recently, a German book on Jürgen Wuchner and his compositions was published by Wolke Verlag, edited by Monika Schießer-Wuchner:
Click on the link and scroll down the page. You see “Bb- und Eb-Stimmen zum freien Download”. If you click on that field, you get the sheet music for Bb and Eb instruments.
I hesitated to make this free download public. I recommend buying the book so the publisher and the authors get their fair share. Even if you do not speak German, there is the sheet music for C instruments. I am writing this article to help proliferate Jürgen Wuchner’s music.