You might try Disney's Guest Services at
http://www.disneyshopping.com... They have a Disney Store Locator... Hopefully, there's one in your area that might have something suitable... Or at least point you in the right direction. You can always call guest services for help too.
I have a Disney Alice Dress that was purchased at Sears (another source for Alice stuff) several years ago... It is labeled 'Disney Fashions - The Walt Disney Company'... Size 5... Very high quality (65% polyester, 35% cotton) and the price was under $30 at the time. Typical Alice blue dress with lace at sleeves and around peter pan color and attached lace trimmed half-slip. Detached pinafore has large embroidered White Rabbit & Watch with phrase: "Hello! Goodbye! I'm Late!" on the bottom half. (sorry it's not for sale)
I've seen the one listed on eBay and elsewhere... Satiney type... Kinda ugly. If you can't find something more suitable, you might consider buying a blue dress and apron or pinafore separately... Download Alice pics/jpgs and print them out on iron-on transfer paper and add your own embellishments. That way you don't only have to use Disney, but have the whole world of Alice illustrations to choose from.
Good luck in your search.
