I've seen a lot of dresses on Etsy, Amazon, and other sites like aliexpress. It really depends on your price range, but if you want a cheaper dress that you can DIY a little bit, I recommend getting a dance dress (I've seen them run from 10-30 bucks) and add some rhinestones on yourself. If you're willing to splurge, Etsy has some really nice dresses and some custom dressmakers as well. Online shopping through Amazon and Aliexpress offer cheaper and expensive options. Although I find Amazon to be a bit more expensive.

Also, what dress you want to buy depends on what you actually need the dress for. If you're looking for a practice dress, you can get a dance dress or a cheaper dress from Amazon. Same with testing dresses. Those don't need to be too fancy and I've seen some on Amazon that are simple, pretty, and relatively cheap (https://www.amazon.com/ACSUSS-Womens-Lyrical-Dancewear-Skating/dp/B07MNYJDD3/ref=sr_1_11?crid=CS45XW1LPEEW&keywords=figure+skating+dresses&qid=1640837380&sprefix=figure+skating+dress%2Caps%2C438&sr=8-11 something like that). However, if you want something for a competition, I would try looking into a custom or more expensive dress that is of higher quality.