It's hard to say how many may still be out there. I think that these might have a higher attrition rate than say a Camaro or a Chevelle.
When I get the chance I google around and find some now and then for sale or in auctions and copy what I can for possible future use.
You have to wonder too how many might have been reworked and they lost model specific things like the horn button center, the decals due to a repaint, swapping of interior paneling due to the plastic disintegrating, and who knows what else. When I see just things like an SOA Nova horn button I have to wonder if the car was scrapped or rebuilt differently and it lost it's SOA identity.
I bought my first SOA to rebuild and a second strictly for donor parts so out of those two only one is still around. The first one was a solid car but the second was to me just too far gone to really save.
Who knows, there may be a bunch of them still around but since there are hardly any reproduction parts a person either has to find an untouched original or scrounge for replacement parts. I know I have been collecting parts for mine for over 10 years and still need things.
I do remember seeing one locally a few years ago not even 3 miles from where I live and after talking with the owner he didn't get it out much.