Here's a good one I've used: https://www.amazon.com/Primal-Pet-Foods-Freeze-Dried-Chicken/dp/B0082C00P8/ref=sr_1_14?ie=UTF8&qid=1497766332&sr=8-14&keywords=freeze+dried+dog+treats
Edit: you can get it cheaper too. My friend buys a different brand in bulk on eBay.
My Boston survived parvo as a pup and has had tummy issues ever since. We feed her Primal. She does really well on it. This was a good resource when we were looking for better food for her.