I traded messages with my brother about this and his recollection is that they first appeared in the early 1970s. Some of the older builders like Clyde Hinkley always used tacks until he retired. Why do you need to know?
It is possible that Old Town Canoe experimented with staples in 1932 but there isn't anyone left alive who can confirm this. They were one of the early adopters of vacuums as shown in the Factory magazine picture below from 1922.