Hello Judy - Welcome to the forum.
You could try eBay (I just looked, there are two options right now, the best is for a set of Jaguar disks, 10.2). But you could keep an eye out for the later model disks. Your eMac came with Tiger 10.4 though it would still run Jaguar. I think I'm right in saying that your eMac would take any other eMac set. As far as I can see the hardware test (AHT) is common across eMac models. Although yours came with AHT (eMac) 2.5.1 I think the earlier eMacs include 2.5.1 which ought to work too, but I'm not 100% sure about that.
If you do buy from eBay, ask some questions of the seller - I think the install set would be 4 disks: 3 grey disks and a fourth AHT disk.
BUT-If a) you don't need OS9, and b) you can live without the AHT and c) you don't need the bundled software that comes on the earlier eMac disks, you could just install Tiger directly from a full
retail Tiger DVD disk - (or
retail Panther 10.3 CDs or an earlier version).
Your eMac has a DVD/CD drive required for the retail disk, and it also would run Leopard 10.5 - although I think a G4 might struggle to run Leopard well, you'd probably be better off with Tiger.
You would get all the main OSX software on a Tiger or Leopard retail disk, all you are missing really is the AHT disk and OS9.
Have a look at *
which is a valuable detailed resource on all early Macs.
Here are a couple of grabs from it with relevant info for your Mac.
*
Whoops - requires 10.5.4 or later 
