I believe Legends tried to remedy this with a solution I quite like. Apparently in the old canon, the Republic realized this during the last stretch of the war, and so they had a company called Sparrti Creations use cloning cylinders that could produce mature clones in about a year with the Fett DNA meaning they numbered in the billions, the trade off being that the Sparrti clones were nowhere near as effective as Kamino clones because they had way less training, horrible accuracy, and could turn on their commanders by refusing orders.

Naturally the majority of those guys were part of the first wave of Stormtroopers, and they actually kept making them if I recall (also being the explanation for modern Stormtroopers fluctuating in effectiveness, because the more effective ones were conscripted or trained)