eBay - it takes some time, you must search. My recommendation is to search for new with tags or new without tags. Don't be afraid to ask for more photos and more measurements. The old saying, measure twice, cut once is true - especially on the internet.
I bought two - yes, two dresses that had never been worn. One had the tags still on - the 1970's vintage. The 1930's dress is my favorite but doesn't show well in photos.
Be wise and be frugal - shop the modern way - eBay.