I became a vampire from the guy in the dark brotherhood. I didn't like the vampirism, so i sought out a cure. I did the cure vampirism quest, and when the count gives u the reward for helping his wife, the reward conversation is still there. I select it again and i get the reward again. i now have 200,000 gold! Woot!
Some "other" ways, at a few of the mages guilds you can buy 1. Get level 20, and they start appearing as random loot on Conjuror/ Necromancer types... Also find them in Ayleid coffers and stuff, in the Ayleid ruins.
Hope it helps, Cadaver
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You're such an inspiration for the ways that I will never ever choose to be.... (Maynard James Keenan - Judith)