Looking for very old Mac OS disc

Hey neighbors, I’m trying to wipe a very old Mac and then reinstall the OS in hopes of selling the machine. I’m told I need the physical discs for the OS to do this. It’s a long shot but I’m wondering if anyone has Mac OS X discs lying around, could I borrow or buy them? The current OS that runs on this machine is version 10.4.11. The processor is a 600 Mhz PowerPC G3. Thanks!