You beat me to it!
That's the story: in the 50's you didn't get a licence for military calibers; and for moose the law required a minimum of 8mm bullet. Thus the 8,2x53R and 9,3x53R were born.
And yes, Sako is the only one making factory ammo for the 8,2x53R.

Incidentally, here's the same rifle "slightly" modified and the latest moose, a decent-sized cow from last season.

- Lars/Finland