Everyone computer savvy enough to have bought the level of card you're looking for (Radeon 9000's, etc) were also savvy enough to be using AGP by then. You're simply not going to find what you're looking for, clearly no one here has something just lying around.
Here's a sampling of what it's gonna cost:
$20 ATI Rage 128:
http://www.geeks.com/details.asp?inv...8P-32P&cat=VCD
$40 Radeon 9000 128:
http://www.geeks.com/details.asp?inv...0-P128&cat=VCD
$45 GeForce FX 5200:
http://www.geeks.com/details.asp?inv...128-CO&cat=VCD
But chances are, you'll have way more success just dual booting a newer PC rather than trying to get some old crappy MB and video card to support OSX.