
San Fierro - Head to the railway bridge connecting San Fierro and the desert.
There are a few locations it spawns in (as well as a hand full of story missions where you can snag one, including Black Project and Misappropriation), but here are the three most convenient ones. The most brutal machine gun in the game, the minigun can mow down hordes of enemies if used right. For those who haven't played the mission, it's just next door to the Burger Shot in Whitewood Estates. Around the corner from the entrance is the chainsaw.
Las Venturas - Make your way to the small warehouse you had to fight your way through in You've Had Your Chips. The chainsaw will be waiting inside the court. San Fierro - Go to the Avispa Country Club and look for the tennis court. You'll find the chainsaw waiting for you by a tip. Los Santos - Go to the small train station in Willowfield and head towards the piles of tires and other junk on the left. Here are some convenient spawn locations. Although this melee weapon is heavy, it does a ton of damage, so it's well worth seeking out. If there's one way to strike terror into the hearts of your enemies, it's carrying around a massive chainsaw, and luckily they're not too hard to come by. You'll find a katana in amongst some palm trees. Las Venturas - Head around the corner from the save point outside the Four Dragons Casino. If you're having trouble finding it, it's the same alley you head down during the Wu Zi Mu mission Mountain Cloud Boys. Head in and then take a left down another alley to find the katana. You'll find an alleyway near the bottom of the street on the right. San Fierro - Head to Downtown San Fierro and look for the Chinatown area. Take the next left you see after crossing the bridge. For those that haven't reached that point in the story yet, look for the Alhambra nightclub in Idlewood and head over the bridge to the right of the entrance. It's behind a fence on the lefthand side. Los Santos - You'll find it in the alleyway across the street from the corner where CJ partakes in the lowrider challenge. Here are some of the spawn points you can find the sword at. That makes it a pretty good tool to have on hand, and luckily, it's not all too hard to come by. The best melee weapon in the game, the katana is powerful, fast and has a long range.