Johann Siebmacher (de.wikipedia.org) published some early books on German coats of arms around 1600 (images from the book from 1605: Wikimedia Commons: Siebmachers Wappenbuch). His name was used in the 19th century for a book named _Neuer Siebmacher_ , a collection of coat of arms that was still in reprint in the 20th century. The website of Bernhard Peters states that 130.000 different coat of arms were collected in 119 volumes. He lists a vast number of digital resources (digitized books).
The German association _Herold_ published a successor, the so-called _Deutsche Wappenrolle_ (75 volumes so far).
If you have a good reason to believe that family Zaun had/has a coat of arms you should turn to a specialized message board like heraldik-wappen.de for further help.
The German Wikipedia entry on Wappen (= coat of arms) has a lengthy bibliography on German heraldry.