Thank you for your help! I'm going to check this out!
Originally Posted by droptopford
Not sure exactly what you're looking for. Your thread title mentions vent window knobs.
You might have better luck finding a complete vent window (handles, button/knobs and all) like these on eBay:
If you're looking for the plastic knob that opens and closes the 'AIR' vent door, I don't see those specifically listed anywhere either. They look exactly like these though: