Does a product exist that would allow me to hang a flush or semi flush light of my choice with a vented ceiling fan? - No. What you would have to do is install a venting fan with a separate light fixture.

But they couldn’t be stacked one on the other right? I’d have to have them offset?

There are all kinds of options of a semi-flush ceiling light/fan combo. Here is one image plucked off the 'net:

There are also recessed light versions:

Would it be thinkable to install sconces on both sides of the mirror and not have a ceiling light at all?