User blog comment:Generale wareagle/How to unlock the X-49, Ui-4045 and XF-900 on the japan version of Ace Combat 3/@comment-2169631-20130216112348

There is 3 ways to obtain the X-49 in the Japanese Version of AC3E:

The 1st way is via the "deadcopy" save file which was given away to VIP's at special Namco events around Japan back in 1999.

The 2nd was via the "Ace Combat 3: Electrosphere - Direct Audio/AppenDisc" which allows you to install the "deadcopy" savefile on to your PS1/PS2 Memory Card.

The 3rd way is if you have a Gameshark device and use the codes which can be found here: http://acecombat.wikia.com/wiki/Ace_Combat_3:_Electrosphere_Gameshark_codes

Also there is some button pressing cheats for use in the mission simulator: http://acecombat.wikia.com/wiki/Ace_Combat_3:_Electrosphere_in-game_cheat_codes