Here's a convenient place to get Omari's Sister's desktop wallpapers! This website conveniently generates the wallpaper in many sizes. Hopefully, you'll find one that fits your needs.
Link to Kuroneko003 portfolio on The Otaku.
I also added this link to the far right had side bar under "Desktop Wallpaper."
Someone requested another ZHD wallpaper...I'll see what I can do about it ;p. I can't promise anything, though.