I'm not sure that it is freely distributable. Knowing Sony, you are probably only licensed to use it if you buy the full PS2 Linux Kit.
Even if it is, the official PS2 Linux is a long dead project. You are better off starting with one of the homebrew open source Linux loaders for PS2, which you don't need the kit to run. It is still quite a bit of work for a mostly useless system though.
If you really want to do it, check out
kernelloader.
