These whistles are not at all uncommon. They seem to range in age from the Rev War period up to probably 1900 and didn't change much during that time. Some were made of bone and even ivory and these seem to be the least common. Some of these whistles seem to turn in in hunting bags, and were probably used in the field. They apparently were in use during the Civil War as well. Some appear to have been factory made and it is possible that the horners made them along with powder horns and aother items. Please post the photos when you can.
Dick