Adding content - 3D model from the internet
There are many online libraries where you can download pre-existing 3d models for use within your project. The libraries range from online repositories for museums and public institutions to marketplaces where 3D artists can sell models they have created for use in video games, medical animation, architectural visualisation, etc.
Paying for models is very expensive and we strongly recommend searching for free options as there are many out there.
A list of libraries and the types of models they stock can be found here.
What kind of model are you looking for?
Image Link - https://drive.google.com/open?id=1NA0HKstZm81JEFGi7s6r9d0y2BcM6FYv\
Depending on the model you want you might need to look for it in a particular library. Some libraries are very specialised and only stock models of a particular type - plants & vegetation, or characters for example.
A list of libraries and the types of models they stock can be found here.