...a fellow customer figured out that 8x56mmR Mannlicher-Schoenauer brass from PPU might be an option. Bought it for a relative pittance, brought it home and it resized and chambered in the Danish Rolling Block just fine.
Yeah, it's 2-thousands of an inch shorter but I don't even remotely see that of an issue, particularly since I have 50 brass for a quarter of the price...
That brass will work just fine. There are other options that will work too but none as easier than 8x56mmR.