John:
I have only ever seen bismuth fours available as shot for reloading, never bought a bismuth factory cartridge in my life!
That would have changed of course, had they been available on the shoot here described, and perhaps Mark has details of the shot size that could have been available.

The twos I use for geese here in the Northern Territory are home-dropped from a modified shot-maker in the manner described on these forums previously,
and published in Guns'n'Game Magazine at the time. I'll try to find the earlier post on this and link it here.

Ah, the link to that article was posted in 2005 and it has now vaporized! I'll find the jpegs and toss them up on my own domain for those interested.

I'm ashamed to say that I smelted several kilos of Eley Bi fours that had been left by a mate who posted south, to drop twos for geese!

These days I alloy bismuth from my hoard of ingots with 5% tin from plumbers' sticks to drop the #2 shot pellets, but can't do anything smaller.