There is the world of difference between infringing an aircraft manufacturer's patent rights and simply creating a 3D software model, the sole purpose of which is to help in the creation of images.   There are some very good-looking 3D models out there, but , if you're wanting to emulate Lockheed's technology, a model from Turbosquid isn't going to help you very much (although, at those prices, perhaps it ought to).

Seriously copying an aeroplane needs an actual aeroplane, or, at the very least, its detailed plans, and the external appearance of the thing is the least of it.   After all, that's a tricky thing to keep secret, when the aeroplane is screaming around the countryside, scaring the sheep and burning up taxes.

Allegedly, the Russians copied a B29 from the ground up, when it made an emergency landing in the Far East in 1945.   They let the plane re-fuel and take off again, but not until they had measured and photographed every last molecule of the thing, inside and out.   Then they set up a production line that worked in feet and inches, so that they could build one.   That's the kind of detail you need to make a serious copy of an aeroplane.  

The idea that the aircraft manufacturers are seriously helping to protect their secrets by pursuing the likes of Turbosquid is plain daft.   It smacks of corporate arrogance, greed and a legal department with too much time on its hands.