I read everywhere that you can only get a fortify skill from Eno Hlaalo in the Morag Tong after completeing his Sanguine Items quest (which took me like 6 hours) or from girl in the Mournhold temple but you have to be a high ranker of the temple. But I also found that a Skaal guy sells these Fortify Skill Spella aswell but you have to progress through the Blodmoon main quest far enough. BUT!...you can also get the spell from a girl in the Imperial Cult area in Mournhold, and you dont have to have any qualifications!!!!!
