Shoes, shoes, shoes! AH!

Greetings!

I am the maid of honor in my friend's wedding.  I have a lot of pain from tendonitis in one of my ankles/back of my foot, and I am having GREAT difficulty fulfilling her instructions for shoes for the wedding.  She has requested that we wear silver, strappy, open-toed shoes, with a strap on the back to prevent flopping. I have tried on silver flats from a number of places, but none seem to have the support I need with the look she has requested.  Many of the flats have no support and those with back straps have a very narrow footbed.  My foot isn't considered "wide," but it's certainly not thin.  I cannot wear heels.

Does anyone know of any brands or stores I can look at?  I really don't want to spend a lot of money, especially because you won't see the shoes from under my dress. 

Thanks so much!

J.