A full sheet of Piso Company 5/8 cent private die stamps is currently up for auction on Ebay. The opening bid price is $159.99. By the description, and from the rather poor photo of the item, there clearly is some damage to this large sheet, though the sheet is intact and complete.
Bob Hohertz has a page on this company and this stamp at his website. He provides an explanation for the apparently missing stamp at the lower right corner of the sheet.