However I dug deeper into the history of these (bavarian) maps and suprisingly found that there are a lot more maps that built the basis of the military maps. And boy, they are uncannily accurate. And of course scattered among archives, survey offices and libraries.
I even managed to find a map with the exact locations of buildings that are still standing today. Manually georefercing them showed that they are often only a few centimeters off.
And to get back to this comment: I had a hard time finding a general map from the same area. And when i found it the office that held the records. They also didn't hold one map, but several maps that were made over the years. However they wwere extremly expensive and I was even bombarded with several limitations. E.g. if I'd publish it in a journal I MUST notify the office with details.
Parent comment is right, that they should be in the public domain, however some administrative bodies still believe that they should be guarded as state secrets, probably because these maps were the basis of tax registers and most of the land units on these maps are still the same 150 years later. Even though the same office publishes WMS data of todays situation for free on their website.