Whether rifles are "supplies" or "reinforcements" is moot as either can be scaled up or down without "retooling" times.
I don't play the 1936 scenario much as knowing exactly what's going to happen years in advance leads to a very unrealistic decision-making situation IMO. In the 1939 scenario, the Soviets certainly don't have too many divisions (to understate things rather considerably.)
Historically, the Soviets lost a lot of divisions to encirclement at the beginning of the invasion, and formed new divisions in time to reestablish their front before Moscow. In the 1939 scenario, the losing divisions certainly happens, but there's no forming new ones. Historically, the Soviets had a draft, so when they lost old divisions they could simply call up old draft years, put rifles in their hands, and point them at the front. You didn't necessarily get good troops that way, but you could form new units fast. In AoD, you can't do this at all: even to form a militia unit requires "retooling" times (no such "retooling" times for switching between replacing tanks lost in understrength armoured divisions and replacing submarines lost in understrength submarine flotillas), and by the time that retooling is done the Germans are in Moscow. This is grossly unrealistic, completely breaks Barbarossa (the campaign is won or lost on the front line, the Soviet Union effectively has no more strategic depth than France), and since as goes Barbarossa so goes the game...
Then, as a bonus, when the AI gets into panic mode it builds militia as singletons, not in queues. This was reasonable behaviour in HoI, but in AoD it means the AI Soviets are spending half the IC they have available for production on retooling... from one militia unit to the next.
But even as a player Soviet Union, while you could certainly have infantry divisions coming off your queues at regular intervals, you can't abruptly call up large masses of men if needed.
