There's a whole forum on Martini Henry's at .milsurps.com. (Add the 'W's.) Including a bunch of guy who were Aussie Cadets.
There's this too.
https://collections.museumvictoria.com.au/items/371716
Note the stock letters mean "Citizen Military Forces N.S.W" The NSW being New South Wales. Made between 1899 and 1949. Used until 1955 only in Australia.
Buffalo Arms wants $51.19 per 20 for smokeless powder ammo. When they have any. Uses a 120 grain "heeled" bullet.
Bertram makes the brass. Graf's wants $38.99 per 20. Also when they have any.