German layout is a standard left shift devided and enter ISO layout so that should not be a big problem, however finding a 100% custom keyboard may be. I haven't seen them, and only a handful of 95%, it's way more common to find 60%, 65% or 75%. KBDFans has some 95% with ISO, but they are out of stock. You may want to consider giving up your numpad and buying an external one or buying a retail keyboard like a corsair or logitech and desolder the switches and put your own.