In Berlin you can rent assistive devices such as wheelchairs, walking aids, ramps and more at the German Red Cross. Information can be found here: https://www.drk-berlin.de/reservierung.html
If your wheelchar needs to be repaired there is a repair service available – 24 hours a day in case of emergency: http://www.rollstuhlpannendienst.de/service.html
Medical Supply Stores
There are many medical supply stores in Berlin. We recommend the following stores: (http://www.ortmaier.com), Medicar (http://www.berlin.de/adressen/rehatechnik/medicar-4f143ac5b4fc475f0bc72b00.html), Reha Team Vital (http://www.rehateamvital.de).