I am sorry. And I guess you can't buy it via the German Amazon site? And these ones?
https://www.amazon.com/Raft-Gateway-Essentials-Book-1-ebook/dp/B00AVUMIDG/ref=tmm_kin_swatch_0?_encoding=UTF8&qid=1564116105&sr=8-1
https://www.amazon.com/Timelike-Infinity-Gateway-Essentials-Book-ebook/dp/B00AVUMIG8/ref=tmm_kin_swatch_0?_encoding=UTF8&qid=1564116144&sr=8-2
https://www.amazon.com/Flux-Gateway-Essentials-Book-3-ebook/dp/B00AVUMIIG/ref=tmm_kin_swatch_0?_encoding=UTF8&qid=1564116166&sr=8-1
https://www.amazon.com/Ring-Gateway-Essentials-Book-4-ebook/dp/B00AVUMIJ0/ref=tmm_kin_swatch_0?_encoding=UTF8&qid=1564116191&sr=8-1