I don't know the details of your situation but I suggest considering following options:
1. Will you fly or take a train from Poland to Hannover? If you go by train, you could make a stop in Berlin (you'll likely be travelling via Berlin anyway) and drop by the Fotoimpex shop at Alte Schönhauserstrasse 32B. They should have what you need. If you go by plane, fly to Berlin and continue by train.
2. Contact Macodirect or Fotoimpex, explain you situation, and ask (beg if needed) to ship your order the same day. They both use good postal services and your order will be delivered next day.
3. Rent a car and make the 330 km round trip from Hannover to Stapelfeld near Hamburg where Macodirect is located. Call them first to ask if they agree to sell you on-site.
4. As a last resort ask around in Hannover's photo stores, they might know if somebody sells it locally.
I hope you'll get what you need.
Andres