re: 1/2 sovs
Some information on AU ones could be found here.
https://bluesheet.com.au/Gold/Half_Sovereign/
You can also by a used book by Marsh, his works
are dated but still have some interesting details
p.s. IMO there is a problem with such sources, they
don't 100% reflect the reality. I.e. liquidity, problems with logistics,
customs and such..