Yeah, something must exist, since the manual explicitly mentions it, and, as correctly pointed out, maintaining thread, task, and interrupt state requires it. Even if you don't care about MultiProcessing (ie what little multitasking exists on MacOS 9), interrupts need to save and restore the cpu state properly.
Since we can't find files, it must either be in the ROM file or in System or hidden away in some other file. On a beige (aka old world) Mac, the ROM file isn't used, so it is most likely inside System, etc. robespierre is right, the nanokernel is likely patched, I'd be shocked if it wasn't.
Regardless, not worth the trouble of trying to find and "copy it", you are far safer just doing a reinstall on top of your existing MacOS 9 as the manual suggests.