Well, there is a Sailor Moon pattern. but it's damn near impossible to find without some serious searching. XD; it's also made for children.
I'd have to say, go with a ice skating pattern (I recomend Butterick 5781 as well) then altering. Choose the one with the line below the bust, then pleat the skirt differently (or not. Depends what you want.) Create a sailor collar, the bows, the gloves, and the little roll-ey thingermagiers on her shoulders, gloves, and around her waist.. and there's your costume. There is a thread that you can post questions on if you have any difficulty with it. It's in the general cosplay thread. "The all purpose, all genere Sailor Senshi costume thread!" or something like that. Very helpful.