I know I'm coming from the other side of this because I work in a bridal salon as a consultant, but I want to say that I agree that in a perfect world, stores could carry each sample in every size, but unfortunately that isn't practical. Samples cost stores a fortune, because they have to buy them from the designers they carry, and in order to carry a decent selection of designers and styles, stores have to make huge investments on new samples twice a year.
The reason most samples are bridal 10s and 12s is because it's generally the middle range that can give the largest number of brides the best way to gage how it looks. It does make it harder for girls who are under a size 4 or over a 16, but I assure you that stores really are trying their best to accomodate every girl that they can.
As far as ordering extra dresses and returning them, it's not like a normal retail store. When a salon orders a gown from a designer, it's being special ordered in a specific size for a specific bride. Designers will never allow a store to return a dress unless it arrives damaged. It costs a lot to produce each gown (in addition to requring several months of production in most cases), so designers will understandably never take a gown back simply because a bride no longer wants it. That means the store would have to eat the dresses, which they have had to buy from the designer(s), and would therefore lose significant money on the sale. Again, it's not practical.
There are however a few designers that spcialize in plus sizes. Paloma Blanca's Diva live, Bara Luxe, Kirstie Kelly for Disney's Red Label, and David's Bridal Women are all geared toward plus size brides.
