This is a doctor I saw last week for another issue. I asked if they could vaxx me and they put me on the list, called a few days later to make an appointment for today.
I also managed to get on other waiting lists by just looking up websites of doctors in my city, emailing and asking nicely to get on their vaxx waiting lists. I send about 20 emails and got on two other lists.
You can also now try vaccination centers, officially they dropped prioritization on monday, but it might be different in your Land or Kreis.