The Atma Weapon

I don't have any pictures, but when you first get it you'll find that it resembles a dirk or another dagger-type weapon. As you progress it will later resemble a sword type weapon. At high levels it resembles a large blue blade that flashes when you attack with it, almost as if there were several being used in one slash.

Where can you find Atma Weapon? I don't remember having it in stock

You find it in the Cave to the Esper World after you rescue the espers from the MagiTek Research Facility.

why would u get such a good weapon (i think) in the middle close to the near end of the game?

Because the weapon isnt a super weapon. As everyone has already said, it levels up with you, so at first it's a pretty normal weapon. The more you level up, the better it gets.

No, there are only two in the game; the one in the cave to the esper town and the one you steal during the final battle.

Um...
I made it to level 50, and the Atma Weapon never really became that cool for me. About one point does it start to be all badass with the 9999s and such?
Because it is a very powerful weapon (If I recall, it does around 3000 dmg or something. But still, maybe not even that), but it doesn't compare with weapons that keep doing 2000 damage when you're at half health and don't need to waste a turn healing yourself.