Take a car down the subway and then ride down the tracks until you see the words say Francis international airport then stop at the train station in the Francis international airport then park up against a wall with a box sticking out of it next park the car next to the wall and jump on the box walk slowly away and then jump into the glitch it will look really weird but that is a good sign that it will work it'll take a LOT of tries but it works
First of all, you have to have all three islands. And you should have at least 50 hidden packages found but that is not required. Go to your hideout in southside hoods in shoreside vale (the third island). And collect the weapons, then, get a car and drive around the back of the building where you got your weapons, you should see an opening and there is a truck. Go towards the opening but don't go through. Then turn around (you should still be in your car) and go back to where you got your weapons, there should be more for you. You can get a lot of bullets and bombs in a short amount of time if you repeat this. And if you get 9999-25 bullets for a gun, you get unlimited bullets for that gun. I don't know if you can get unlimited bombs for a certain bomb.
For a pistol, simply kill a cop or gang member and grab gun.Next is the machine gun, go to the top of Saint-Mark's hill by the restaurant, there is an alley, walk down the alley and there will be passages through walls, at the second passage enter and walk down a little and you will see a gun. Next is the rifle, go to to the fire department and walk towards the city and turn down the street, there will be a hill, then by there an entry to go to the train station, don't go up the stairs, continue walking around the building and the rifle will be in the corner. Next it the flamethrower, go to the train station I was previously was talking about and walk on the tracks toward the left and walk until you see a building top, walk until you see a floating gun and jump on the dark step and jump on it and walk into the gun. Next is a war gun, go up Saint-Mark's hill and then go on the street where in the middle there is a space with a mafia sentencing car and walk along the wall until you hit another wall and there be a space, go threw and walk down the ramp, there's your gun! Last is the fire bomb, go to the SUPA SAVE store and go to the old train rails and walk/drive to the middle until you see a group of people kill them and get the bombs! That's all I've got.