That may be harder to achieve than you might think. Big sellers would have lots of employees inside Germany and smaller sellers may be reluctant to setup a multi-national business...
Assuming we're talking about German language content, it's likely small sellers would exist in Austria and Switzerland servicing that market. Furthermore, it wouldn't be terribly difficult for someone small to medium sized who doesn't specialize in German language content to include such content in a larger library.
All of this is absurd in an age where anyone can just type "hardcore porn" or any of myriad more specific requests in to google.
Yep. Amazon, Kobo, Apple, and Google (55% of the ebook market) all have operations in Germany. They cannot pull out, and nor can the local sellers that account for 40% of the ebook market.