This is one of those things where I can't remember which came first, the chicken or the egg. (The outfit or the occasion?) All I know is that 1) Usa was planning a photoshoot for her senshi in Central Park, and 2) on a trip to Fashion Bug to spend a gift certificate my grandmother had given me, I happened upon the PERFECT outfit to match the outfit Rei wears in the “all red” drawing in the fourth Sailor Moon artbook. I would’ve bought it anyway, even if we hadn’t been planning a photoshoot--I like the styles Naoko draws for the girls, and think they suit me far better than the “designed for women who resemble celery stalks” clothing that’s in most stores now.
So, yeah. I realize this barely qualifies as a “costume”, in that it’s entirely store-bought, out of a regular clothing store, and it’s just a “street outfit” that the girls wear in one lonely artbook image, but I thought I’d add it here, in that a lot of people do "casual" versions of the Sailor Senshi, and I did base it on an actual existing image.