The Elder Scrolls Store (thanks Thomas) now offers the promised new dungeon
quest for Elder Scrolls IV: Oblivion. In the old days they'd give away the razor
to sell the blades, but in this case you'll have to pony up $2.99 for Mehrunes'
Razor. Word is: "Conquer one of the deepest and most challenging dungeons in all
of Cyrodiil to claim this fearsome weapon."
Ummm.. Mehrunes Razor came with the original game, it was just not available anywhere in the world. All you have to do is place it somewhere through the construction set. There are already many mods that add Mehrunes Razor...