It's been awhile sense I has to go through this, but my Tigger went through this and hated the food the vet gave us. So we did find low ash food at the stores for him. It's just been so long, I don't remember the name.

But I do know if you take the time and read the bag/can you can find something. Just look for anything with a ash count of 2.5 or lower. I use to read every can/bag on the shelf till I finally found what worked and what he would eat.