Where can I find my ideal prom dress?

My prom is roughly just under a year away and it's the only one I will have as my school only holds one at the end of the year for those in their last year at school after graduation so I really want my dress to be special! I'm a complete girly girl and I'm looking for something similar to the dress Hilary Duff wore in A Cinderella Story. I've checked loads of websites and have seen a lot of really beautiful dresses but nothing has properly caught my eye yet to the extent I'd consider buying it. Preferably a UK website/shop but anywhere is fine :) hope you guys can help me out, thanks!!