Nightwolf's alternate costume is in the Netherrealm. (A-4). You have to fight him for it. Good luck. It's not that hard though.

ok ive looked everywhere in A4, near the wall and lava, but i cant seem to lacte NightWolf...to fight him, where is he? does he only appear at a certain time?

Go to the other side of the wall. I got it when I beat Konquest, but I'm not sure it's necessary to do that first. But, check the other side of the wall. I aslo did a mission for him and returned somthing to him... I forget what it was though. Maybe you have to do that first? I'm not sure.

I went to the other side i cant seem to find him, arggg....but on the other side of the wall... there seems to be a gate at A-4 and behind it a ladder up a tower...is there anyway to ope the gate, is nightwolf up in the tower?

Oh now you are on the wrong side. That's weird that he isnt there...

There's a side mission you have to complete before Nightwolf appears at A4.
I believe it's the mission where you have to return something that was stolen from him in the Netherrealm. Find Nightwolf at C5, when you enter the gate to the lower plains of the netherrealm, he's to the left of the door, as soon as you walk through it I believe.