Here are the submission guidelines for every comic and manga publisher...super helpful for any aspiring writer out there.
Turns out that I don't even need an artist...if the script and idea are strong enough I can submit just the writing to some companies and they will pair me with someone. I am going to try this approach too, because I believe in me. I believe in the product and I believe I have the skills to write a good fucking comic. So there.
Oh, and Dark Horse has some good comments to make about formatting.