I'm not too sure about the flu vaccine, as it's currently "out of season", maybe you can try to send an email to the doctor to ask, or perhaps they'll have one in stock to administer to you at the exam.
For the covid booster, I got mine at a pharmacy, so try calling every pharmacy within a wide radius to check if they still administer those boosters.
Your GP might know of locations that still do as well.
If you don't mind driving to Limburg, I can tell you which pharmacy I went to.
Good luck 🙂