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It does excist, its an blade that consists out of 2 parts, if you have both parts Cromwell (the dwarf in the Docks District) can forge it for you.

Item locations:
Silver Blade: You get it from Saemon Havarian (Brynnlaw) when you have control over the Pirate Ship
Silver Hilt: You get it from a Githyanki named Kruin, if you have the Silver blade in your possesion, he will find you in Athkalta with a war party and demand the Vorpal Blade of you, this will end up in a fight and he has the hilt as loot

Go to cromwell and he will mention the Vorpal Blade parts in your inventory and will ask you if he can forge it for you, accept, now your the owner of the Vorpal Blade
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Here you go (use ctrl-A to highlight the text)