Very cute anime-style Cure-Marine dress for Aiko4 released by 赤まむし ("Red Viper"), link at his gallery over at the Japanese pixiv website.  His link goes to a google docs zip archive, from where you may download the item.  Again, I am unable to post Red Viper's link explicitly here, for Renderosity ToS reasons.

BlackKnight has done a render of this dress:
http://blackknight.way-nifty.com/poser/2010/06/post-0864.html
This link is safe to go to, I believe. Just scroll down until you see the render of the girl with the bright aqua-marine hair.  That's the dress in question.
Same webpage also shows - see last render - the cute bikini which Mammomammo has just released ( see Mangaka-online's post above ).

Eternal Hobbyist