I looked through my entire store, the lowest protein treats seem to be sweet potato chews. There is a particular one from Sams Yams called Bichon Fries, which are made for the smaller dogs.
Sam's Yams Bichon Fries Sweet Potato Chew - Luke's All Natural Pet Food
There's a lot of different opinions about what to feed pets and humans that tend develop urate and or calcium oxalate stones.
A lot of people recommend a low Oxalate diet and use this as a guide
The Low Oxalate Diet