So as we all know, there are a few people in the Rocky Horror world that can create custom-made, screen-accurate costume bits, for a price.  However, I do want to suggest Etsy.com for costume bits as well!  Specifically using Etsy's Alchemy section -- it is rather like a reverse auction.  You list what you want created, and your ideal price -- and others "bid", much like contractors bid on jobs.  You can preview the people's past sales and what they currently offer before choosing any one.  The best part is, if you don't see any worthy bids, you don't have to choose anyone to do it.

This is how I got all my new costume pieces created, and at very decent prices as well.  I got my dinner scene corset made for $75, as well as my floor show corset.  My silver and black cape with stand up collar was created for $35.