Tl;dr catch an Electabuzz in Platinum on Route 222 and breed it.
Elekid is not obtainable in the wild in Generation IV without dual-slot mode. Electabuzz is available in Platinum, HeartGold, and SoulSilver, so you will need to catch one and breed for Elekid.
In Platinum, Electabuzz can be caught on Route 222, which is first accessible after you complete the story in the Distortion World. In HeartGold and SoulSilver, Electabuzz can be captured on Route 10, which can only be reached once you enter the Johto Hall of Fame. Electabuzz is also more common on Route 222 than Route 10 (20-30% vs 5-10%).
You will eventually need to advance the story farther than the location you get Electabuzz in either game, so ultimately it probably doesn't matter that much. But Platinum is definitely the way to get Elekid as early as possible.