FWIW based on what I've read, the slings and ammo pouches included in the CAI accessory kits are in fact original Soviet items, but they're mostly postwar-era and were never issued.
The Soviets relegated the Mosin-Nagant to reserve duty after WWII upon adoption of the SKS and later the AK-47 as their standard service rifle. Most 91/30s sold recently by milsurp importers were refurbished for reserve duty during the 40s and early 50s, and the accessories mostly date from this same period.
Some of you may be wondering why the Soviets would go to the trouble of making tens (if not hundreds) of thousands of accessory sets for rifles that would probably never be used. A single word is adequate to explain the reason:
Communism.