Oblivion Mages Guild Questions

So I was just cast out of the mage's guild while doing the final thieves guild mission for killing a fellow member. I was almost done with the quest, so i didnt want to reload from a previous save point. Well anyways, what I've gotta do to get back in is retrieve 20 Daedra hearts, and 20 Vampire Dust. I found the daedra hearts, that was easy. But where the hell are all the vampires? I've seen probably 3 in the whole game, including the one in the dark brotherhood. Where can I find my 20 Vampire dust and get readmitted to the mages guild??????

i already finished the thieves guild missions.  i AM the gray fox!!!!!  YES! 

And I finished the dark brotherhood missions, i have all the relics of the crusader, I'm the arena grand champion... all i have left is 14 oblivion gates, the main quest, and the mage's and fighters guild missions.  i have done probably 4 or 5 fighters guild missions, and the last mages guild mission i did was the Vahtecen.