Origin版のDead Space 2にてHardcoreモードをクリアしたが、
Hand Cannonがインベントリに出現しなかった。

"C:\Users\%username%\AppData\Local\EA Games\Dead Space 2\"にある

Here's what those three bits do:

Controls.AcL.X, bit 16:
Achievement: Made Us Whole
Description: Complete the game on any difficulty setting
Unlocks: Riot Security Suit
* this one works as it should - if you've completed the game, it should already be set
* this is also what puts the completed Marker in the main menu
* also needed to unlock Hard Core mode, along with Game.PDiff = 1 and Game.Played = 1

Controls.AcL.X, bit 17:
Achievement: Mission Impossible
Description: Complete the game on Zealot difficulty setting
Unlocks: Arctic Security Suit

Controls.AcL.Y, bit 14:
Achievement: Hard to the Core
Description: Complete the game on Hard Core difficulty setting
Unlocks: Soldier Suit, Hand Cannon