If you don’t find what you are looking for on VintageDancer.com you can probably find it on one of these two lists:
Have a look through Etsy.com and eBay.com as well. Be very aware of too-good-to-be-true deals on cheap websites, even with amazing reviews. Many reviews are fake, customer service is non existent, return shipping expensive etc. These deals really are too good to be true.
If none of these have what you want, you may want to have it custom made for you. This will cost more and take more time, but it may be the only way to get the item exactly as you want. Also, most costume designers on Etsy.com will take custom orders. Search for something similar and send them a message to see if they do custom.