You can.
Get the weapon, import to start over.
Then start over in the making your character screen,then start the game, and pause in the darkness before the Ah the Child of bhaal has awoken speech. During darkness.
Then drop the blackrazor and when you start the game in the dungeon, pick the weapon up and you got it.
If you dont understand, Ill be glad to try and clarify.
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Coffee anyone?