While the full AROS source tree requires SVN access, Buildable AROS sources are available anonymously through two methods:
1.) nightly source and contrib source code download
2.) Anonymous git repos AROS.git and AROS-Contrib.git at repo.or.cz
If you want a GPL'd Amiga OS replacement, start writing one. That's not impossible, Its just a lot of work. Software licenses like AROS Public License seem to encourage entrepreneurs who think they'll make some money off the work by value adding to them in various ways and being able to keep some things to themselves if they wish for a "competitive advantage in the marketplace", kind of like ...um imica or ares.