How to get OS 9 (Classic) installed on an os X machine

I am migrating old files from an old Mac that ran OS 9 to my new G4 that runs OS X. How can I get the OS 9 system on my G4? I do not have any OS 9 installation discs.

OS X 10.4 should have Classic Mode included. OS X 10.5 or later no longer has this mode.
Classic Environment - Wikipedia, the free encyclopedia

You can use an Emulator such as SheepShaver for Classic mode:
SheepShaver - Wikipedia, the free encyclopedia

Depends on the model G4, last version of MDD, FW800, cannot run Classic. Also be aware when the current system was installed, it was necessary to select 'Install OS 9 drivers' at the time of format otherwise no go. Should this be the case, you may be up for a format and clean install. You will need to purchase a full retail install version of OS 9, preferably OS 9.2.2, the last version released. Do not buy the silver grey system specific discs.