Update: think you need to register first:
https://accounts.unrealengine.com/register/index
Is it just me or is the source not public yet? https://github.com/EpicGames - No public repos
Is it just me or is the source not public yet? https://github.com/EpicGames - No public repos
Also, they would be required to allow GitHub users who weren't UE4 subscribers to create forks, which is a violation of their licensing terms.
Public GitHub repos just aren't really suited for projects that aren't open source.