ILwrath is right, the source code to AmigaOS up to 3.9 is pretty much 68k assember (so it can't be ported to other CPU's) and, from what I understand, in a very bad state.
Also, I belive, the source for the OS eariler than 3.1 has been lost.
The AROS sources are freely available though, and if it weren't for the ease of downloading a Kiskstart ROM from the net (:-(), they would have been used to make a free kickstart for Emulators etc...