I think you should learn more about corona, it have material library what you can use, for more complex material you can use this
https://www.sigerstudio.eu/xsmpmax-landing/or
http://coronamaterials.com/but most materials we creating myself.
As for models, corona also have material converter what can convert to corona from most common render engine like vray, so you can use vray models
3dsky.org most cheapest models, but not all good or evermotion volumes, though i advice to check materials after conversion