The iMac G4 .. fondly known as the "iLamp" .. lol.. is a great machine.. I have one
and I love it.
I believe the largest hardrive they came with was 80 GB. As far as Ram.. Apple specs say max of 1GB .. however.. that's because at the time, there wasn't a memory stick any greater than 512 for the iMac. I've got mine maxed at 2GB .. 1 stick on the accessible slot and 1 stick on the internal slot (I had Apple certified techs to that).
As far as finding one.. unless you go thru E-Bay, it might be tough. I've seen them occassionly at Small Dog Electronics. Perhaps if you can get your hands on a MacWorld type magazine .. that would help as there are adds for places that sell used/reburbished Macs.
Good Luck!!