It's not a TM in gen V so your best bet is a pokemon that knows by level up or follow this guide to the move tutor (attached)
You get the Iron Tail TM by going up the waterfall in Meteor Falls and then going up a ladder.
TM 23 Iron Tail can be found in the Iron Mountain.
TM 23 - Iron Tail can be found on Iron Island.
After beating Jasmine, she will give you TM Iron Tail.
Iron Tail isn't a TM in the game.
iron island
In the Pokemon game corner
jump on a bike and eat its tail
Defeat Jasmine a olivine city.then youll get iron tail.
get TM23 (iron tail) in iron mountain
iron tail
most likely 42, easy to do if you caught it at victory road good moves to teach it are ice beam, blizzard ,hyper beam and iron tail,trust me been playing Pokemon for years