What could it be made from? What's close...? Anything?
It looks like the Sig hibreds... Steinel Ammunition Introduces 8x22mm Ammo for Nambu Type 14 and Type 94 Pistols
I searched further and found a thread. I'd actually do this as I have time...and a ton of forty brass and 30/30 dies.
Reforming and Reloading 8mm nambu