Ebay. I believe you want to play PS2 on your PS3 right? Get the one with 60GB hard drive instead of the 20GB, because 20GB done have a built-in Wifi adapter.
@dynashox, you do not need the earlier version of playstation 3 to play "Ps2" games on it, you can have any of the latest version.
If you can play PS2 games on the PS3 that mean you've purchase the earlier version of the consoles. The 20GB and 60GB is the best one to choose because you can play the PS2 games through a hardware emulation. The old 80GB version also can play PS2 games but this time through a software emulation. Some PS2 games will not work properly on this version of PS3. The latest version (40GB, new 80GB and 160GB) can't play PS2 games as Sony have removed the PS2 graphics processor from the console to cut the cost down.
Here we go again... @ Wrongfully Convicted : As dynashox said, eBay is probably your only chance - but be prepared to pay a bit extra for an old BC PS3. You could probably get a new PS3 AND a used (and chipped) PS2 for around the same price.
I too would check out ebay...however the earlier ones had a few kinks in it to work out...I had to send mine back twice.
The reason why I have not purchased a xbox 360 is because I have a lot of ps2 games that I would like toplay on my ps3.