Yeah, you need to disenchant an item that has the fortify enchantment. Be wary of the "Fortify *magich school* and magicka regeneration" though, as having the combined effects in one enchantment weakens both effects, and you won't be able to achieve -100% that way (well, maybe with boosting, but that's a whole other discussion). The mage robes *generally* have the double fortify/regen effect; at least those that you purchase in the College of Winterhold do.The best way to find items to with the proper enchantments, in my opinion, is to go to a store that sells the items that would theoretically carry the enchantment. I just sit in them, check the stock for what I need, wait 24 hours, check again, wait 24 hours, etc. until I can buy my item. You can get the enchanted items through loot or drops, but that could take ages.For conjuration I went to "War Maidens" I believe, and eventually bought a helm of conjuration. It is a relatively rare enchantment.