I am sure you already know that Top Shop do almost everything in size 6 and petites go down to size 4 - also River Island do 6.
This website is a French company called Promod - very keen prices and a good range. I have bought things from them when in France & Italy and the quality is ok. I have also bought from the website.You can return things if they don't fit or you don't like the. You can search on their advanced search page just for size 6. Suggest you don't use the colour column - just size & dress, or top or trouser etc. If you roll your cursor over the picture you get a closer look at the fabric/pattern.
http://www.promod.co.uk/search/search-form
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