You can learn it at the Gates of Limberry Castle from the assassins Celia and Lede. You need some advance preparation though. You need to equip Judo Outfits, which cancel their instant death attacks and I think there's a second status ailment that they can cause that you can block with the right equipment. Immobilize both assassins and move Ramza into spell casting range of one of them. They would rather attack than not attack, so they tend to cast Ultima under those circumstances.

I'm not sure if you have to have a second character also in range (I know you do to learn Zodiac).