Trying To Upgrade to OS X 10.5 Leopard On iMac G5

Apple has long stopped distributing OS X leopard discs and and upgrade to leopard is vital for me. I'm aware that they're sold on ebay, but to great inconvienance. Coming from a windows PC, I was surprised to find such lacking support to upgrade to leopard. I don't understand why it can't the disc image can't be distributed through the internet, even in return fir money if apple still wants to make profit off of it.

Besides the lack of support my powerpc mac really needs the upgrade and I've come to ask, is there an alternative way to upgrade to leopard without having to buy a disc off of ebay?

Thank You.