The only 3 monitor AGP card capable of running games of that kind that I know of is the Matrox Parhelia. It it somewhat old now, and will not be capable of playing the newest games.
However, that card is designed for 3d applications. If all you need is 3 screens for desktop, multimedia, photoshop etc, then you can do it much cheaper. Most AGP and PCI-E video card already have dual monitor output, so thats 2 screens. for a third screen just add a PCI video card on top of that. You can run 2 video cards without any problem. If you wanted you could use a Matrox G450 Dualhead, or similar, for your 2nd card and have capability for 4 monitors.
You are only limited by the number of expansion ports on your motherboard, and the number of outlets you have near the computer for all those monitors

.