Fluff's got it right.
The ejector is an absolutely critical part that regulates things like head space, end shake, timing, and alignment.
Revolver parts do NOT just "drop in" like many auto parts, and are individually factory fitted.
Even if you managed to find an ejector, it will be a used part previously fitted to a different gun, and will not fit properly.
For this reason, S&W restricts these parts and will not sell them to the public.
For a repair, return the gun to S&W and they will replace the part for a fair price.