You could try the "cabbage soup diet" :
www.cabbage-soup-diet.com/eating-plan/
But as far as I can tell- the best "quick loss diets" usually consist of drinking or eating tons of non-starch vegetables, broths, and loads of water. Fruit juices are ok... except they can have a large sugar content.
I am going to give you a disclaimer though- On almost any "quick" loss diet you will be running to the bathroom A LOT. You'll also probably feel fatigued and hungry as heck on day 2 or 3... but it will get better. Yes, "crash diets" are not good for you - but honestly... doing a few in your lifetime will ruin you either- After any diet like these... try to GRADUALLY increase you calories to avoid "yo-yo-ing" too much.
Because you are not really losing "fat" there really is no guarantee that you wont still look like a "sausage" in your costume. -if the day draws near and you don't look better- go to grandma's standby and throw on a girdle or slimmer!
Good Luck!
-M.