I need help finding a dress?

I'm attending a lot of formal parties with the upcoming season. I'm 15. A size 2 or 4 and flat chested. I need a dress for a quince, a church banquet, and a friends personal formal at her house. I live in texas, so it won"t be too cold. I'm looking for knee length, in black, dark blue, shades of purple, or an emerald green. Any links will be helpful or places to look.