You might call Kesslering's or Lynnwood Gun. I know Lynnwood Gun had mebbe 25-40 rounds a few months back.
You can get new production ammo though, as well as brass. You will need some clips as well, unless you want a single shot. Numrich and Sarco both sell the clips, ammo pouches, bayonets and other accessories. Supposedly these things kick like a mule! I've owned two and never had a chance to fire them.