New owner new questions!

Hi Everyone,

I have just taken ownership of a RV4, it has the following style air vents on the right hand side of the canopy skirt.



However the one at front the black/open close twist knob is broken


I would ideally like to replace/repair this so it is functional again and wondered if you could help me where I would get that part.

I also eventually need to add some additional cooling/vents but that is a different discussion.

Thanks

Karl