You'll find Classic on your installation CD/DVD that came with your Mac. If it came with multiple disks, it's almost certainly on one of the later disks.
The reason you won't find a download link is this: Classic is actually a full-version of Mac OS 9 running side-by-side with OS X, allowing you to use older programs that never received an OS X update without having to restart your computer. Needless to say, Apple would rather not post a free copy of OS 9 on the internet (though I'm not entirely sure why: they offer downloads of every system up through 7.5.5, but none later than this).
Oh, and out of curiosity: what program do you need classic for?