A good, although not 100% successful, strategy for tracking down both original-language editions and modern translations (English or otherwise) is actually the Wikipedia article on either the author or text. In this case, it led me to:

Adam von Bremen, The History of the Archbishops of Hamburg-Bremen, trans. Francis Joseph Tschan, 1959.

Worldcat is down right now so I can't see which libraries have it, but it is digitized through ACLS if your library subscribes to that.