When it comes to diatonics, Hohner does offer exchange parts (i.e. a brass plate with a full set of reeds). Haven`t seen this for Chromatics, but you could ask if they could send you one for yoour instrument (but be prepared that it might be almost as expensive as a new harmonica of a cheaper variety).

Contact adress can be found here:

http://www.hohner.eu/index.php5?1393

Good luck!
Ernest