There are canine nutritionists who will formulate homemade diets for different health problems for you. The one I know of is Monica Segal
. I was on her nutrition forum for years until it switched to Facebook, which I don't do, and I have both her books on canine nutrition. There are others who formulate diets specifically for a particular dog.
I really empathize, as I have one dog I feed a raw diet to just because no kibble (and I looked at dozens) doesn't have at least one ingredient she's sensitive to, which in her case brings on itching which brings on hot spots. If, as I suspect, you can't find a kidney specific kibble without something your dog is allergic to, homemade, raw or cooked, is another route to investigate. I fed a cooked homemade diet to my last Rottie for years after the Chinese melamine scandal.
You might also search for a forum specific to dogs with kidney problems. When I had a cat with crf (chronic renal failure), I found a forum like that for cats. My cat would not eat any of the feline kidney foods, and lo and behold someone had compiled a list of the regular cat foods that had the best protein and phosphorus percentages for crf cats. Toes lived to 20 (5 years after diagnosis) eating those non-prescription foods.