Hardaway's Alabama Battery at Gettysburg had Whitworth's located about where the Peace Monument is now. The greatest weakness of the Whitworth's seemed to be in their carriages which if they were the English ones were not up to the strain of firing.
There is a Whitworth on display at New Market, so I would assume that a battery there might have had at least one? A cursory search only identified the three batteries as having "rifles" in addition to other ordinance.