There is no simple answer to finding a short. A wiring diagram would be helpful. That would give you an idea what is on that circuit and the direction the circuit goes. Then you can start disconnecting each component until the short goes away and be inspecting the harness as you go.
Being it's an ATV, good chance it is a burned or crushed wiring harness. Look underneath, any area that would be subject to damage from road debris. Look around the exhaust system for melted wiring. Check pivot points around the steering, suspension, storage compartment lids, etc. There are a lot of wires in the handle bars. Look where the wire harness goes into the handle bars, look where the accessories attach to the bars, has something been hit, come loose and twisted cutting the wires?
Here's a hint, steady poking fuses in is going to get expensive. Make a jumper wire to TEMPORARILY bypass the fuse but DO NOT LEAVE IT CONNECTED! You're only going to TOUCH it across the fuse and watch for a spark. As you go through the shorted circuit disconnecting components, touch the jumper across the fuse and see if it sparks. If it still sparks, it's still shorted. But be careful! If the jumper wire gets hot, your leaving it connected too long!