Yeah, the Ditto part is hard. I would suggest breeding between your dittos to get better dittos (closer to flawless). I was lucky myself, and had very little trouble amassing a collection of Dittos to breed with on my pokemon Emerald.
Once you get dittos that will work, start trying out spreads. There's not much else to it. You may have to breed several of each thing that you RNG, to get the right parents. But it is really worthwhile.
Find anything for the Giratina, or no?