Doing a quick search I think it could be a default mac wallpaper so if you are on mac then you already have it. If not then just look up a collection of all the mac wallpapers and download it there. It is hard to tell what the wallpaper is with it being so small and the center being covered.

Found it, unfortunately the original is only up to 1280 x 800 resolution, however there is a tutorial showing you how to make it so you could easily upscale it by remaking it from scratch if need be.
http://www.idblogr.com/2011/10/mac-os-x-lion-login-screen-inspired_19.html

Note, don't post saying you can't find it or saying other people will help. That's completely pointless and replying to it saying it's pointless is almost as pointless...

Anyway...marking as solved!