You will not find them all in one location. Some people upload to FlightSim.com, others to AVSIM and some even add them to other websites that only keep them on there for a short while.
However, Captain Sim does list (many of) them in the Free Liveries section for the 777 (Check-in to Your Profile > Product (777 Captain (777-200)) > Get Free Liveries), but they take you to external web sites. They used to store them on the www.captainsim.com site, but not any more. :(