need old mac os installation disc

I work in a Canadian university and we received some donated old computers. One of them was an iMac G5 (the last PPC model, 20 inch, from ca. 2006). It would be enough to handle basic office and internet browsing needs, except that the previous owner had removed the hard drive. I found a replacement hard drive for it, but couldn't find a MacOS installation disc old enough to work with this machine. The last supported version is 10.5.8 Leopard (not Snow Leopard). I tried various Linux versions, but they are painfully slow for actual use.

Since this is an obsolete computer, we don't plan to spend any money trying to buy parts or services for it (yes universities are penny pinchers 🙂). That's why I want to try the user community and see if someone would be kind enough to donate his installation disc. If I can't find one this machine will eventually head for disposal, which is quite wasteful considering it still has a decent screen size, memory, and processor power.

Thanks for helping out.