Andreas, Connie,

you are correct that Mrs. Asche is the expert but she has retired end of August. Another expert is Dr. Ernst Otto Bräunche but he is also retired.
Nevertheless, I would recommend that you write to the municipal archives, archiv@.... 
Since I am in contact with Mrs. Asche I can forward her requests (privately) but I doubt that she is able to help without having all the papers.

Good luck and best regards,
--
David Seldner, Karlsruhe, Germany
seldner@...