Where are OSX end-of-life announcements?

I have an old G3 iMac with 10.3. I'm looking to justify a request for a new one. I basically need to show that security updates are no longer being provided for it. I can't run a newer version of the OS as far as I can tell.

Can anyone point me to an announcement on the Apple site identifying 10.3 as being no longer supported (or the contrary if that is available)?
Thanks, Patrick

Message was edited by: Patrick123