I'm not sure that PrimeFaces was open-source back then. It started out originally as a purely proprietary product.
So you might have to pay Prime Technology to obtain the source. That's assuming that they'd even sell it to you since I doubt they'd want to support it.
It isn't just that that version of PrimeFaces is that old, it's that I'm also pretty sure that you'd need
JSF Version 1 to run it and that, also is obsolete.
Moral of story: Anyone who thinks "software doesn't wear out" is fooling themselves. There's more than one way to wear out something. Budget accordingly.
The secret of how to be miserable is to constantly expect things are going to happen the way that they are "supposed" to happen.
You can have faith, which carries the understanding that you may be disappointed. Then there's being a willfully-blind idiot, which virtually guarantees it.