The friend of mine has 8x60R double rifle and he has bought couple of dozen cases in Germany, but it was long time ago. As I remember Sebastian, when he used to work in Belgium told me they reloaded 8x60R from time to time.
I'd suggest you to try to find small shops in Europe, who reload vintage ammo. No chances to find this ammo or cases even at large companies such as S&B or RWS.

Geno.