Hey Britt - congrats on the upcoming quinceanera!
If you've already tried Ebay, you could try Yahoo Japan auctions English website here:
Yahoo!JAPAN Auctions - International - Fashion
The Japanese version of Yahoo auctions has a lot more items, but it's harder to use if you don't read Japanese:
Yahoo auctions in Japanese!
Search for "ドレス" (dress) in the auction search engine for some results.
Or, you can try Rakuten:
Rakuten Online Shopping
You can also search for dress (ドレス) on Rakuten.
If you want to buy something from Yahoo Japanese auctions or Rakuten, there are many companies who will buy it for you and ship it to the US - but you do have to pay them a fee for the service. Here is an example of one such service for shopping at Japanese websites:
Japan Auctions Center
Good luck!
