Old Mac Powerbook Upgrade

I’ve just come across an old Mac Powerbook G3 of the early design prior to USB. It has OS9 on it and I’m trying to upgrade it to work as a music storage and player for the wife. I put a 40Gbt. HDD in it and that works O.K. but I’d like to buy and use a PCM/CIA card that would give me 2 USB ports. this I’m finding out only works with Mac OSX 10.0 or newer. What are my alternatives?
Where can I get the Mac OSX full version? the Apple web site says my machine can only handle up to version 10.2. that’s O.K./ but I have yet to locate a downloadable package that I can buy over the Internet.
Help me out her someone, please!!!!

Jimbo