I don't know if it's official or unofficial, but here it is:
Quake 3 Arena sourcecode on GitHub:
https://github.com/id-Software/Quake-III-ArenaIt seems Travis Bradshaw is in charge of this process, and he has also published a few other sourcecodes there on GitHub, including Doom 3 and Doom for iOS:
https://github.com/tbradshawhttps://github.com/id-Software
