According to Raymond Fredrich's book "Nail Pullers", these are "hardly found". That being said, I got one in a lot of nail pullers at Donnelly’s this summer.
Again from Fredrich: "The Fulcrum Shoe is Charles Maynard's design patent no. 27,571 August 24, 1897. It was assigned to Dexter W. Goodell of Greenfield, Mass. The patent for the complete tool is unknown."
There was another company, C. A. Maynard & Son of Springfield, Mass, that also used the same fulcrum design patent. Also "hardly found".
Mike