When I took my Theological German class in seminary, we used Jannach’s “German for Reading Knowledge” Heinie & Heinie, 1980 ISBN 0442256965 It too is out of print, though.

One suggestion: use a wiki to write and publish the book. Limit access to those you approve, and then let people update and change as they wish. wikipatterns.org did exactly that when they were writing their book.

That way, it would free you up to focus on making changes, rather than being the person who has to cut and paste changes.

Let me know if you need to know more!

Peter Enns, Learning German as a Research Language: An Introduction for Students of Bible, Theology, and Related Disciplines (ms in progress, no publisher yet
contacted)

http://peterennsonline.com/wordpress/wp-content/uploads/2007/11/CV%20current.pdf