The only eraser strips that are still manufactured that will work with the Electric or Cordless erasing machines that accepted the 3 1/2" or 7 " strips are the Pentel ZER-2. 

Also for use in the Pentel Clic Eraser

The Pentel ZER-2 Eraser strips are 3 1/2" soft white vinyl strips and are sold per pack of 2 strips.