Where can I find the new loading spashes (SR/HA/TT/CS) in 1920X1080 resolution?

Does anyone know where I can find 1920x1080 versions of all the latest loading screen backgrounds for Summoners Rift, Howling Abyss, Twisted Treeline and Crystal Scar. All the ones that I've found seem to be in all sorts of odd resolutions that do not look good when trying to use them as a Desktop background.