quote

"Location : Tsunade in her office [07].
Reward : Sasuke's Kunai
Mission : Right after you have done Sasukes part of the Master Mode Tsunade
will tell you to form a team consisting of Naruto, Sakura, Sai and
Yamato as their sensei. Get back to Orochimarus Hideout and enter
the infamous locked door, it will be unlocked from now on. You'll
have to get through all rooms another time. At the last room you
have to fight a group of really strong bandits. When you have
finshed them go to the end of the room to receive Sasukes kunai."

quote Des - FAQ

When play through the game you will see a of lot characters standing around
with gray Konoha symbols above their head. You can fight these npcs to get the
them for Versus Mode (if you haven't started with a savegame from a previous
game) and unlock assist characters. The list will show you where you can find
each of them. Not all Clones are there from the beginning, so if a special one
you're not there when you start just check back later after you finished some
other clones.

Note: 5 Clones cannot be found until you clear Sasukes part in Master Mode
along with going with Naruto through all the rooms. After that you can
find 4 new clones (marked with * behind the names in my list) near and
in Orochimarus Hideout. After you got those the final clone of the 4th
Hokage will stand on the Hokage Office in Konoha.