Two Bloodgrass: This is the tall red grass you see everywhere in Oblivion and at some Oblivion gates, and it can be bought in some alchemy shops as well, so it is easy to find.
Six cloves of Garlic: Many homes have these lying around on the dinner table or stacked somewhere else. Almost every home in Skingrad has some bunches of garlic (often 3 or 4), most often hanging from a beam in the basement. Or get one and duplicate them.
Five Nightshade leaves: Nightshade is prolific throughout the West Weald. You can also find some (or maybe all) at "The Main Ingredient" in the Imperial City Market District, the only alchemy shop guaranteed to have Nightshade in stock. The Arcane University has several growing there as well.
Blood of an Argonian: Melisande gives you a special Enchanted Dagger to use and collect the blood. You do not need to actually kill the Argonian, just stabbing your victim once with the dagger is sufficient.