Good question..and I have no idea, I haven’t actively searched for freeware airports in years.
Back in the FS98/2000/2004 days I used to scour the Avsim and Flightsim.Com libraries.
I currently have a handful of payware airports and GSX. I started collecting payware airports for P3D during various sales before I made the transition from FSX.
Once FS2020 was announced last year I pretty much stopped investing in P3D add-ons.
GSX provides enough “life” and customization at the default airports to where it’s good enough for me until FS2020 comes along.
MC