What are the sources or from where do all Auto Portals/Car websites get their data?

You say ALL... which certainly on its own means there is no answer.. because its impossible that every one gets their data from the same places, in fact most have unique sources for most of their data.. And that's from first hand knowledge...

The online stores are somewhat less diverse... but they get theirs from databases provided by wholesalers they work with... but with the store front and pricing data tweaked enough to make it their own as far as the end use is concerned.