He doesn't have one. The only other Atma Weapon in the game is a steal item from the 'girl' section of Kefka's Tower. Since this is part of the final battle, you will only be able to use it against Kefka due to an inability to save.
You can use them in the final fight, but train others too just in case. And it's too late to get the first Atma Weapon. However, turn Ragnarok into a Sword and bet it for the Illumina at the Colisseum
Yeah, sadly enough he doesn't, which is wierd, considering he IS the weapon. Stealing from Atma Weapon gets you an Elixir, I believe. And to use Atma Weapon, you can only throw it/equip it to someone in the middle of battle.

If you fight Kefka at any levels below 50, Kefka's tower will kill an average of 3 people on the way to the top. So put your best as 4-7, not 1-4. And Illumina is the best weapon in the game, because of its stats and ability to randomly cast Pearl, and avoid back row damage limitations. Atma's damage is based on HP, which means its not as useful until level60+, when you have both the Strength/Vigor/HP Stats to let it do 9999.

Um, I have Bismmark, like 4 blanks, then Seraphim. So I don't have it. So I guess I steal it huh.
You are missing Golem, ZoneSeek, and Palidor. Golem/Zoneseek are actuioned off at the auction house in Jidoor. Palidor is found on Solitary Island, after you go back with the Airship.