Bookworm nailed it. If your car needs end links or bushing check out rockauto. If your car doesn't have a sway bar at all check out wrecking yards. Any FWD 03-08 Vibe or Matrix front sway bar will work. They should all be the same diameter.
The AWD cars have thinner front sway bars.
To install the front sway bar check out this thread, and the two threads linked there.