Jack Brooks built a rifled English trade gun years ago, based on a period reference to a damaged English trade gun that was restocked with a rifled barrel. There was an article in Muzzle Blasts, I think October 1994, about the trade guns he made, although I can't remember if the article referenced the rifled trade gun or if that tidbit came from some other source. Either way, there is apparently one period reference that would justify an early pattern trade gun with a rifled barrel, albeit as a non-original modification.