This turned up on Google News:
"What happens to the costumes after the show? Randall Christensen, the designer, sells the garments on his Web site. Christensen issued a press release before this season began, and it said dresses from Dancing With the Stars have become available online for purchase to dancing enthusiasts at his Web site, a trend he intends to continue. Right now, only dresses for seasons two through five are available, although many have been sold. Those from season five are priced between about $2,000 and $5,000 each".
Article:
http://www.msnbc.msn.com/id/24456940/
Randall Christensen's website is here:
http://randalldesigns.net/
There's an illustrated catalogue of dresses still available from season 5 on this (huge) page:
http://randalldesigns.net/sp-bin/spi...E=59&CATALOG=5
Would it fit? I notice that all Julianne Hough's costumes are size S, and Mel-B's are all size M/L.
It seems to me that quite a lot are "still for sale". I wonder if the ones being sold are actually copies that he's selling.