In the dungeon with the imps in Act III, where they mention getting a great weapon to kill the evil man, I found the unique scythe they were talking about (labeled in green "unique scythe - defender" or something), and then when I cracked open a barrel right next to it, I found ANOTHER unique scythe - defender (not very unique, I guess), but the second one was clearly a staff, not a scythe. Neither appears for sale on the merchant screens.
