The white dress is actually very close to Yuki Cross' white dress.
Here are links
as for the black dress.... let me get back to you on that one.
(edit) As for the black dress, since no specific characters I know usually would wear the black dress, you can always think about other characters you may know that MIGHT go for that look. So you can be a formal Vocaloid Miku or something. : 3 Good luck!