gamespro

Best answer as chosen by Asker / Ratings
You will find Yuffie in a secret area near the pagoda. You will see a building with a bell inside if you ring it a secret path will open up and you will find her there.

The huge materia can be found in these locations.
The underwater reactor in Junon.
Fort condor.
Corel reactor.
On the rocket in the rocket town, the password to get it is circle, square, x and x.

Cloud's - ultimate weapon is obtained by defeating Ultima Weapon.
Barret's is obtained by taking him with you when you go to fight Hojo in Midgar you will find it in a chest just before the fight.
Tifa's - is obtained from the vending machine in the inn at wall market, to get there you will need to get sector five key to enter Midgar again you will find this in the bone village. Go there and look for normal treasures in the top of the area. Go back to the vending machine in wall market and you will get Tifa's ultimate weapon.
Red XIII's - after you take Bugenhagen to the ancient city go back and talk to him in Cosmo Canyon and you will get Red XIII's ultimate weapon.
Yuffie's - is obtained from the sunken Gelnika in the generator room.
Vincent's - is obtained from the cave west of Gold Saucer. To get there use the submarine and go towards the Nibelheim area and you will find another cave when you go through you will be allowed to go back up and you will be in the area where the waterfall is, have Vincent in your party and go in on disk 2 then on disk 3 go back and you will get his weapon.
Cid's - is obtained from the rocket town after the rocket is destroyed talk to the guy that is always looking at the rocket a couple of times and you will get Cid's weapon.
Aeris's - in the temple of the ancients go through door IV in the clock room.
Cait Sith - when you go back to the shinra HQ again when you go back to Midgar go to the 64th floor and it's in one of the lockers.