corn free dog food

I need help finding a free dog food corn is also a "formula of the stone." Please help!?
My dog has a history of bladder stones …. recently underwent surgery to remove them. She must remain in a food "formula stone" the dog the rest of his life to help prevent stones from recurring. At this time is eating Hills CD Prescription Dog Food. She also has skin yeast. I think you may be allergic to corn and I like to try it in a food that is corn free, but must also be a "formula of the stone." There are several brands that lead to the formulas of stone, but all that I have found corn. HELP PLEASE!
my neighbors dog has stones and swears by this food dog. said he got it from your vet in the south but was not available in the Midwest (which is a snowbird) anyway – I'm not familiar with indgredients but on this link to Royal Canin. Where can you find more information. Additional http://www.prescriptiondiets.com/ Note: Dogs with kidney stones and early-stage renal disease are usually low-protein diet to BARF diet is not a good idea for your dog.
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