I had never heard of the Martini Henry Cadet before your post,,,
A quick Google search verified your information,,,
Many were indeed converted to .357 Mag.
I did find one listed at Gunbroker,,,
But $1,495.00 is out of my range this week.
I guess I'll have to settle for my break-open H&R Handi-Rifle,,,
That Martini Henry action is just soooo danged sexy,,,
I had dreams about emulating the movie Zulu.
Thanks for the info my friend.