User blog comment:WalkingonAyr/Mizuki Academy Model Needed!/@comment-27060102-20151012192812

https://www.assetstore.unity3d.com/en/#!/publisher/5437/page=1/sortby=popularity This person makes rooms for games and such. You can save the images.

and I know a website with mostly 2d backgrounds but might have some 3d backgrounds http://sdt-bg.esy.es/index.php?/category/1.

also mmd stages http://mmd-stages.deviantart.com/gallery/38505273/Educational-Buildings