Well, not to be personally critical, but that statement is not really historically correct for most of the historic period.
Though the major reason most American Gunsmiths used imported locks prior to the AWI was the large shops that specialized in making just locks in England and Europe could make them so much cheaper, it was also because GOOD steel was so expensive and especially for springs. This does not mean GOOD steel was not available, it was just very expensive and original accounts show the type of steel preferred for springs came from Sweden, Norway and to a lesser extent Germany and Switzerland. Even English gunsmiths bought their spring steel from those countries with a strong preference for Swedish and Norwegian steels.
Now, I have not been able to document AWI and Post AWI sources for spring steel, as to when U.S. production of high quality spring steel became readily available. As much as I have studied State and U.S. Armories from Rappahannock Forge through the U.S. Armories at Springfield and Harpers Ferry and large civilian contractors, the subject of steel and especially higher quality spring steel is very rare to almost non existent.
However, rest assured that gunsmiths and gunmakers did not waste their time and money on questionable steels for springs and frizzens and later on other parts, except in the most unusual circumstances.
Gus