You might be hard pressed finding one that fancy for £300, all those details are hand-beaded and they have to be made to measure.
Try searching for 'classical tutu', 'pancake tutu' or 'Russian style tutu'.
to be completely honest with you, I would go into an upmarket ballet shop, and either pretend to be a ballerina or pretend to be a mother buying one for her child. However, I'm sure there are online shops which sell ballet costumes. This one, however, if it was for a professional production, may well have been hand made... just take a look around the interwebs, see what you can find.