I've got a 1999 Blueberry clamshell iBook an I want to get it up and running agin. I'm wondering if I can get Mac OS 9 or OS X on it and more importantly where I could buy the software.
The maximum OS version is 9.2.2 for Classic Mac OS or OS X 10.3.9 (Panther). I'm not sure which one to recommend. OS 9 might be faster, but OS X is certainly more powerful and will be far better supported by software (though Panther is so old that you'll have to use old versions of many apps).
You'll probably have to go digging on Craigslist or eBay for install discs that old.
It's a long-shot, but you could also check with independent local Mac shops to see if they still have old copies of OS 9 or OS X for sale (Apple Retail almost certainly will not). If nothing else, you could probably pay them to get it up and running again, which would include reinstalling the OS if necessary. However, checking it in for service would most likely cost much more than finding an old copy you can purchase and install yourself.
Other than that, you'll probably need to follow CajunLuke's recommendation of checking Craigslist and eBay.