The 'ground' textures at Pattonville are amazing. They must be 32bit high resolution and had to have been low altitude photos. I know that when I fly around that airport and looking away, turn back to see it, the colors blink for a bit a base color, and reload the textures (FS2004, low ram, 32Bit computer). So that tells me the textures must be 32bit high rez instead of 16bit, etc.
Finding good sky photos can be hard but there are a ton of outlets of them out there. I am sure one of the pro's will chime in soon.
The most difficult is getting permissions... They know the FS scenery guys want their work now and some will demand some high prices, while others could care less, though their photos probably arent nice.
Another thing, is that you could possible 'make' your own, if could find similar types of fields and things. You could copy/paste freeware photography over zones on a 'overlay' ground terrain piece of work, making the texture to look real when its sectioned from other sceneries. A parking lot for instance is pretty 'normal' and generic. You just need to make sure it blends 'perfectly' as an overlay in the textures creation.
Touching up photos with precision is a nice art. Making oil stains, shading around tree's onto the grass, shading around building sides, etc...
Bill