A couple of observations, prior to the Revolution, very few barrels or locks were made in Colonial America...Barrels came from both the Germanic areas as well as England, we know this from the records that the Moravians kept...If the gunsmith wanted a rifled barrel, they were rifled here, in America...So, if you had a customer that wanted a smooth rifle, it would be easily made from the barrels in stock also...Were they ordered smooth because the gunsmith knew not all customers would want rifles??
Another observation...After 2-250 years, how do we know that barrel that is now smooth was originally rifled?? Remember, they were made from iron, not steel and those that were used quite a bit may indeed have been rifled, bored out, refreshed, etc...
Were there smooth rifles made in the Colonies, sure, how many? What percentage would have been smooth originally? Nobody really knows...