In order to find the local authority offices in your town you can consult the homepage http://www.meinestadt.de/

Just enter the name of your town on the left and click on Go!

About half way down the side which now appears, under "Schnell gefunden", you will find a category "Rathaus & Verwaltung". Click on this.

Underneath you will find the category "Stadtführer". Here the first entries to click on are always the official homepages of the towns themselves.

On each of the towns' own sites there is a category "Rathaus" or "Stadtverwaltung".
This is where you can find the offices and authorities you are looking for.