After all, they managed to keep Kamino and all that quiet for years. But the obvious conclusion is that they had been ordered under the radar. None of this is stated in the films, of course, they just magically appear when needed. Some may also have been produced on Kamino as well, though I'm not 100% on that. Once the Wars started, the Republic placed their own orders- Sifo-Dyas' orders had mainly been for the initial production run of Acclamators, walkers, and so forth. From what I vaguely recall the story with the Republic military during the Clone Wars was that Sifo-Dyas was manipulated into ordering their materiel as well as the clone battalions.
