I did an inspection earlier this week where neither the garage, kitchen, and add-on porch fan had a switch. The buyer’s realtor is asking me whether this is legal? I know that we are not code inspectors…but does anyone know how to best answer this question?
It is okay to say that you don’t know. Additionally, you are not a code inspector but one could call the local AHJ to inquire, if they wanted to. 
Is there an additional ceiling light in those rooms?
There’s no requirement for ceiling fans to have a wall switch.
Dom.
In the garage there is an additional ceiling light and in the add-on porch area there is an additional light. None of the fans have lights on them.
Only “code” I’m aware of is habitable rooms and bathrooms require a switched controlled light, this may be a switched receptacle except in kitchen and bathroom.
One wall switched lighting outlet at garage.
One outlet at exterior side of doors.
Ceiling fans typically do not require a wall switch, you may want to check with the local authority.