You could try Austrian Bakery on Clark. Obviously, it's not German, but they make similar old-world style bread there. It's worth a shot.
Also, I'd recommend sampling some of the better bakeries in town when your boyfriend gets here. As Cathy said, Germany is very regional so he may be accustomed to eating different breads when not in Berlin. I think as long as the quality and craftsmenship of the baker is top-notch, he may find a new favorite.
Austrian Bakery
2523 N Clark Street
Chicago, IL, 60610
(773) 244-9922