if debugging is the art of removing bugs, then programming must be the art of inserting them..
These 60 sites are great, In addition I use http:www.findfiles.net where you can find and freely download more than 100.000 dwg AutoCAD files (at least that is what they claim there).
Yobi3D is a 3D model search engine. You can search with simple keywords and see the results in 3D. https://www.yobi3d.com