In Grand Theft Auto: San Andreas for the PS2, PC, Xbox, and Xbox 360, there are a couple weapons you can duel wield by getting to a certain level with that particular weapon.
Here is the list of weapons you can duel wield with once you hit the required rank:
Dual Machine Pistols – Get Hitman rank with the Machine Pistol
Dual Pistols – Get Hitman rank with the Pistol
Dual Sawed-Off Shotguns – Get Hitman rank with the Sawed-Off Shotgun
Dual Tec-9’s – Get Hitman rank with the Tec-9