This weapon is located at Happiness Island which means you'll need to get hold of a helicopter or boat to get there. If either of those two options aren't availabe you can always swim there. At the island go inside the first door of the 'Statue of Happiness' and there will be a security guard there with a carbine rifle. All you've got to do then is Kill him to get the Carbine rifle. This weapon cannot be fired from cars and can kill with two headshots in Multiplayer and Single player and is highly effective during Team Deathmatch.
At the TW@ Internet Cafe log into a computer and enter the URL 'www.libertycitypolice.com' and select the 'Database' tab which is located at the bottom of the homepage. When you do this you will be able to view the Liberty City Police department files on ALL the characaters in the game.
Enter any of the following codes when Roman has given you his old mobile phone to activate the corresponding effect. You don't have to wait long before you receive the phone and the codes can be entered as often as you like.
To enter the codes into the mobile phone press 'Up' to raise the phone higher and reveal the complete keypad. Then use your controller to select the set of numbers according to which cheat you want to use, after you have entered the code the cursor moves to the dial button, just press 'Up' again and if successful you will see a message 'Cheat Activated' on the screen. When a code has been entered correctly, a new 'Cheats' menu option becomes available on your phone under 'Options' which allows you to access the cheats without having to enter the phone number again.
It is advised not to save your game after you have enabled a cheat code.
To input these codes (with default controls) press the up arrow once to bring up the cell phone and once more to enter manual dial mode. Then dial one of the numbers below for the effect mentioned. (note that the first time you put these in you need to wait for it to ring, after that there will be a cheats menu on your phone and as soon as you choose it in that menu it takes effect.
Remove wanted level: 267-555-0100 (i think you can only put this in the first time while you have a wanted star, best to do it somewhere the cops can't get you so you have time) Full health/armor/and some ammo (it also gives a weapon set, if you are missing weapon types, and changes any you do have to weapons from that set): 482-555-0100 Spawn police helicoper(annihilator): 359-555-0100 Spawn turismo: 227-555-0147