I buy our CET chews at the vet's office, but you can find them online too.
Warning: they are a potential choking hazard. Wylie's Mom almost lost one of her pups when he choked on one.
Because of that, I hold the chew while my boys work on them. I also use the medium size for my big boys. The chew can turn into a rubbery potato chip like thing and potentially be swallowed, causing the choking hazard.
https://www.chewy.com/virbac-cet-enz...FUIfhgodgeQEfQ