Seeing that you're German, too, I would suggest that you try to reach out to some newspapers. I know that's extremely old school, but it worked well for us. newsaktuell.de/ots is a service where you can send in a press release (and pay) and they'll distribute it to newspaper reporters for you. Also, they offer "Native Advertising" which is basically that you write an article about yourself and they'll pretend as if it was objective news written by them.

And lastly, did you know that you can contact your local IHK and they will report about you in their membership magazine? You probably already pay for the IHK and you probably already get their magazine. A calender seems like something that other CEOs would want to hear about, so this might actually be great content for their magazine. And just like you, every other company owner is also a mandatory IHK magazine subscriber ;)