How do you get spiritomb with NO CHEATS?

Answer 1

In Pokemon Diamond, Pearl, and Platinum:

First, go to the Underground. Mine for an Odd Keystone. Go to Route 209 and place the item in its spot. Now here's the tricky part; you will need to talk to non-COM players a total of 32 times. You're done in the Underground now. Equip your team with the right Pokemon. May I suggest Pokemon around Level 25, and either a Dark or Steel Type? Both of Spiritomb's types will do minimal damage to them. Go back to Route 209 and approach the Hallowed Tower, where you placed the Odd Keystone earlier. You will battle Spiritomb immediately. Weaken the Pokemon and throw a Pokeball.

In Pokemon HeartGold and SoulSilver:

Spiritomb is found in the Pokewalker location Quiet Cave.

This Pokemon must be traded to any other Main Series game to be obtained. It can't be obtained at ALL in the Generation I, II, and III games.