Iron Tail does not exist in PokéPark Wii. The game uses Generation III (Ruby/Sapphire/Emerald) move data. Iron Tail debuted in Generation IV (Diamond/Pearl/Platinum).
Each Pokémon has 1–2 moves from Gen III learnsets. Examples:
Play Pokémon Diamond/Pearl/Platinum (DS) or later. Pikachu learns it at Lv 50 (DP) / Lv 45 (Pt) / via Move Relearner.
Bottom Line: PokéPark Wii = Gen 3 moveset. No Iron Tail. Master dodge + type advantage + partner swap.