Federal has the right lead free ammo for you. One example is this Ultra-Shok Heavyweight Waterfowl, designed to take down those big birds. This variation, in 12 gauge, has a 3" shell loaded with 1-1/4 Oz of #2 lead free shot which it fires at 1450 fps.
Heavyweight is simply the densest available shot type in the industry. At 15 g/cc, it is better than its closest competitor by 2 on the density scale. That kind of density allows downsizing of shot, more pellets on target and extreme energy. Ultra-Shok Heavyweight will not use the FliteControl Wad like its turkey hunting counterpart, to allow for optimal patterns on waterfowl.
100 rounds per case.