In GTA San Andreas, there is a glitch that will cause CJ to be able to be controlled without a head. To exploit this glitch, start a multiplayer game, making sure Player Two has a Katana. At any point during the session, use Player Two to behead Player One, terminating the multiplayer session. CJ will remain decapitated for the remainder of the single-player session, except for during cutscenes. To revert to normal, reload the game.
El Quebrados, Tierra Robada - Behind a small building in the trailer park in the north part of El Quebrados. From the El Quebrados Safehouse, head north and cross the street. Once you cross the street you should see a black, white, and blue trailer ahead of you. Go to the north end of this trailer and turn left. You should see a small building that does not look like a trailer. The Katana is at the north part of this small building.