Possible Duplicate:
Where can I find the source code of Ubuntu?
How do I obtain the source code for Ubuntu 12.04 LTS i386 32-bit?
Possible Duplicate:
Where can I find the source code of Ubuntu?
How do I obtain the source code for Ubuntu 12.04 LTS i386 32-bit?
There are multiple ways to get the source code for Ubuntu.
You can browse to the online archive archive.ubuntu.com
You can download it through apt apt-get source 'packagename'
If you want the kernel, I'd start at http://www.kernel.org/
The problem with wanting the 'source for Ubuntu' is that the distribution is basically made up of a bunch of different packages. I'd probably narrow down to what packages you want to look at and go from there.