All Pokémon have six IV stats with a value ranging from 0-31. 31 being perfect, 0 being useless. Every Pokémon has IVs. You are looking for a perfect (31) Defense IV. There are several ways to do that.
1 – DexNav Chain – As your search level for a Pokémon goes up, occasionally you will see white stars in its preview. Each of these stars represents a perfect IV. One star means one perfect IV, two stars means two perfect IVs and threee stars means three to six perfect IVs.
2 – IV Breed – Find a compatible parent with a perfect Defense IV (you can find out your Pokémon's perfect IVs from the IV checker by the Battle Maison). Give that Pokémon a Power Bracer and breed him with Goomy. The Bracer will guarantee that his perfect Defence IV be passed on to the newborn Goomy.
3 – Ask Around – There are plenty of people who either have a breedject Goomy with a perfect Defence IV or will quickly breed one for you.