Where is Central p2 repository, that has all Eclipse and 3rd parties plugins ?
All third-party plugins are available through the MarketPlace, and will reference all the p2 sites.
For Eclipse itself, you would see the list of p2 update sites for all Eclipse distros at the "Eclipse_Project_Update_Sites page".
There isn't just one p2 site which would reference everything, but the Marketplace automatically creates a combined update site with your own favorite plugins, if you create an account on the Eclipse Market Place website.