Cels Forum

Well...what you're looking for are painted backgrounds from 
Ghost in the Shell-not cels.  The reason a cel exist is because animation is happening.  Only animated things have cels, where as backgrounds are usually paintings and because there's only one of them (as opposed to hundreds of cels) probably WAY more expensive and hard to get a hold of...if you can find background paintings from Mad House or anyone else it would likely be at a convention.

Good luck