[lizajuk]

As far as I know. London isn't the place.
There are actual shops, as opposed travelling bazaars and web sites, in Manchester: Whirling Dervish, Edinburgh :Hilary Thacker and Forbidden fruits in the Midlands. I think there is also one in Yorkshire.You can get addresses from their websites.
There may be shops on the Edgeware Road that sell a few costumes but probably not what you are looking for.
Londoners may know better, of course. And then again Antwerp ain't that far!