Hi, James -
Your G5 is not OS 9 bootable, hence any stand-alone OS 9 Install CD will not be uasble.
The only source for a 'real' install of Classic is from the original disks which came with your machine. It is a good idea to have such a set available as long as you have the machine; if nothing else they are a perfect start when it is needful to do some trouble-shooting with a hard drive.
Apple's Customer Support sometimes has replacement original disks available; the newer the machine, the more likely they will. You can contact them via the applicable phone number in this article -
http://www.apple.com/contact/phone_contacts.html
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Since your G5 is not OS 9 bootable, you do not need a bootable OS 9 install in order to use Classic. Also, unlike OSX, OS 9 is Finder-copyable (drag-and-drop copy) - it will retain its functionality.
This means you can copy a working OS 9.2.x install from another machine, and use it as Classic.
You can also copy a System Folder from an OS 9.2.1 Install CD; such should work, but in a very limited way - the System Folders on OS 9 Install CD's have a very limited assortment of extensions and control panels, and as a result many services would not be available.
Although OS 9.1 is the minimum usable OS 9 version for Classic, it may not work with the recennt version of OSX you are using; OS 9.2.x would be a much better choice. Relatedly, an install of Classic on your model is not upgradeable - the OS 9 download updates run only when the machine is booted to OS 9.
Your best choice would be to get a replacement original set of disks, and use those.