MIG welding is now called 'GMAW'[for Gas-shielded Metallic Arc Welding], and the filler wire is always fed through the torch, and used to strike and run the arc.
The other common inert gas-shielded welding technique, which the Yanks refer to as heliarc, is now termed 'GTAW', for Gas-shielded Tungsten Arc [formerly known here as TIG, for 'Tungsten Inert Gas']. This uses a fixed tungsten alloy electrode in the torch for running the arc. Filler rod is fed in by hand. This is the technique of choice for aluminium repairs, as it's much more controllable. Also, it saves having to buy a large spool of wire for each alloy to be welded, as is necessary with GMA. Various shielding gas mixes are used for different metals; straight Argon is usually the choice for aluminium.
Most welding workshops will have a GTAW rig, but as grumpy says, aluminium welding is a specialist skill within the trade of welding.
