Ever considered the 10,75x68 ?
I´m just planning to build one.
No problem in findig barrel, loaded cartridges or reasonable priced components for reloading.
Energy is between 9,3x62 and 9,3x64 but fires a 350 - 400 grain bullet. (energy is not everything)
You can even use a .404 rimless barrel and have some more bullets to choose from.

Tom