SPOILERS!!!
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Robe Of Vecna can be bought from bonus merchant in the Adventurer's Mart (Deirde's her name IIRC). Amulet Of Power is given to you by Aran (the ShadowMaster.. forgot his second name
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when you pay Gaelan Bayle, or can be taken from Aran's dead body if you side with Bodhi.
And why do you need MR? It can be lowered BTW.