taken from -
http://www.gamefaqs.com/console/psx/file/197341/27656
V. Permanently missed list
A list of things that can be permanently missed.
__Materia__ ____Location___
Ifrit* Cargo Boat
Ramuh* Chocobo Jockey Waiting Room
Added Effect Cave of the Gi
Morph* Temple of the Ancients
Luck Plus Temple of the Ancients
Bahamut* Temple of the Ancients
Neo Bahamut* Crater
MP Turbo Crater
W-Item Midgar Train Tunnels (Second Disc)
Steal-as-Well Missed by missing Leviathan Scales
MP Absorb Wutai mini-quest (pre-3rd disc)
Phoenix* Fort Condor final
Bahamut ZERO* Missed by missing any of the Huge Materias
* These materias can technically be gained by beating Emerald WEAPON and tak-
ing the prize to the Kalm Traveller. However, they'll just be part of some
master materias, so it's better to get them by themselves.
__Equipment__ ____Location___
Yoshiyuki Rocket Town
Princess Guard Temple of the Ancients
Javelin Gaea Cliff
Poison Ring Crater
Battle Trumpet Underwater Reactor
Scimitar Underwater Reactor
Rising Sun Steal from Diamond WEAPON
Aegis Armlet Midgar (Disc 2)
Starlight Phone Midgar (Disc 2)
Max Ray Midgar (Disc 2)
Glow Lance Shinra HQ (Disc 2)
HP Shout Shinra HQ (Disc 2)
Missing Score Midgar (Disc 2)
Umbrella 5000 points/Gold Saucer Speed Square (Disc 1) (UNTESTED)
Shotgun Rocket Town Weapon Shop, pre-airship
Oritsuru Missed by missing Leviathan Scales
Curse Ring Mideel pre-quake/Steal from Ultima WEAPON 1st encounter
Warrior Bangle Steal from Eagle Gun on coal train
Shinra Alpha Last chance: Submarine battles
Ziedrich Three times steal from Rude (Rocket Town, Gelnika,
Midgar tunnels)
Touph Ring Two times steal from Reno (Gelnika, Midgar tunnels)
Behemoth Horn Shinra HQ disc 2 (on stairs)
Pile Bunker Shinra HQ disc 2 (chest in item shop)
Master Fist Shinra HQ disc 2 (chest in item shop)