Skyy Vodka ad The Antagonist #54.
who designed the dress and where may it be purchased ?

Since I can't answer this as an "answerer" I will add it in the
comments...I emailed Skyy about this and received a response quite
quickly. The text of the email is below. I will post again if they
provide me with any more information.

Dear ***********,

 Thanks much for contacting SKYY!

We have had an overwhelming response in regards to that dress!  The
dress was only produced for our ad and is one of a
 kind.

However,  due to its popularity, we have just begun negotiations with
a national retailer to make the dress a reality.

We will absolutely keep you up to date with further information!

Until then, please keep checking in with us at www.SKYY.com.

Cheers,

The Team at SKYY