Where can I buy a "fortify magica on target" spell? I used the one in the room by the pillar so now I need another one as I didn't have all the spells to begin with. I'm an evoker with the mages guild and need to move the pillar in the cave.

That's a tough one. I know you can buy the 'Sever Magicka' spell from Sulinus Vassinus in the Skingrad Mage's Guild. Being a Restoration spell, I would imagine that 'Fortify Magicka on target', if it can be bought at all, might be available either in Anvil or in one of the Temples. If you don't want to search all over Cyrodiil for one (and who does?), just leave the cave and wait three full days (72hrs). The scrolls in the chest will re-spawn. Hope this helps.

You should be able to buy a Fortify Magicka from these folks: Marc Gulitte, Edgar Vautrine, Raminus Polus, Ungarion. Then just go the spellmaking altar and make a custom version of it that is ranged.

I think there is only one fortify magicka on target in the game and that if you lose it you have to make one yourself. (or re-load a previous save) - I generally duplicate it just in case I mess up - plus it is great later on for helping your allies in melee battles like Kvatch, Bruma, or when you have to save brats from Oblivion gates or goblins.