My local gunshop (F&OW) got me a 5kg bottle of bismuth fours, imported from Falcon in New Zealand by DRC Imports in Victoria.
Like all these things, there's good news and bad news...!

The good news is the availability.
The bad news is the price:
getting up towards a hundred bucks a kilo!
I was a bit taken aback by this until I noticed the pellets are all tin plated!!

Can't imagine why they would do that, probably doubles the cost!

I can understand tin-plating steel shot in the UK where field-shot birds may hang in the window of a game dealer for days before being sold,
and steel pellets could begin to rust within the meat...
but bismuth is relatively non-corrosive and non-toxic to humans.

Why the hell would the shot-manufacturer tin-plate bismuth shot??

I'll try to find out where Falcon get the shot pellets from, and also whether it can be sourced unplated at a better price.

Meanwhile, at over 3 bucks a shot just for the pellets, I'll be limiting their use to very special duck outings with the Rigby sidelock!

If your chambers are 2 3/4 with modern nitro-proof, it's cheaper per trigger-pull to buy the Falcon factory loads than their bulk shot pellets! How silly is that!