I'm not jailbroken so can't access the contents of /var/stash or wherever it is Apple keeps their stock wallpapers.
I'm kind of a bit OCD and have recently grown fond of the iOS 6 palm leaf fabric wallpaper - which I have set on my iOS devices. Can't find it anywhere online though, to enable me to set it as my OS X desktop wallpaper. (What can I say - I'm going through a green phase after learning that green is the colour most easily processed by the eye). Retina 2048 x 2048 would easily cover my 1920 x 1200 macbook desktop.
Anyhow if anyone can help out, is much appreciated.