Acceptable attire for "Black Tie" wedding

I have a Black Tie wedding coming up at the end of the month. I seriously looked in every store on Long Island for a gown. Is there a rule that you have to wear a gown to a black tie wedding and besides the following stores, where can I find a dress? I will even buy something online, if I knew where to look.

Stores I already looked in:
Nordstroms
Bloomingdales
BCBG
Lord & Taylors
Macys-I found one there, but for another wedding I have in Sept.

TIA!!!

Re: Acceptable attire for "Black Tie" wedding

You can get away with a knee length cocktail dress with dressy shoes and nice jewelery.

Re: Acceptable attire for "Black Tie" wedding

IMO - it doesn't have to be a "gown" but it's probably a good idea to wear a full lenth dress. If not, then like the PP said, a knee length dress is probably fine, so long as it's fancy and not something you would wear to a dinner and cocktail party. My wedding was "black tie optional" (mostly because I didn't feel comfortable telling people how to dress, but the RH did call for it), and there was a decent chunk of people who did not wear a full length dress and I didn't see a big deal with it.

HTH