Well, strangely enough, though I don't have much opportunity for ducks and geese, I know what I'd use.
We have public lands here in Iowa where non-toxic is required even if just pheasant hunting. I came upon Kent Tungsten Matrix, which is somewhat spendy, but what isn't that's any good? it has a density just below lead's 11.34 g/cm3; IRRC, about 10.-something. It's also of enough polymer, that it's "soft" and safe for vintage guns and tighter chokes like lead is.
Their 12 ga. load scoots 1 1/4 oz out at 1525 fps and due to its density, it smacks birds like lead. Kent also offers this in about all the usual gauges.
In the Midwest I look to Mack's Praire Wings in Stuttgart, Arkansas for the stuff.
That looks like really good stuff, but I need 3 cases and my boss will kill me if I spend $1200 on shells.
