I also know Daur Don kennels Andrey is a great man and breeder, I have a CO from him and even is 8 months old right now, is a great dog. He also breeds CAO and he has serious dogs. Here you have one of his males: That dog is 94 cm at the sholders so is very big. Andrey was planning to mate that dog with this female: You can also consider the kennel Talisman, is a Russian one located near the borden with Ukrania. I have 2 pups from Talisman they are just gorgeous. Here you can see the father of my pup: This dog is 93 cm at the sholders. And this is the mother: Now, these are hard dogs so you have to consider your experience with this kind of working dogs. There is this kind of association of Ukranian breeders under the name of Security Dogs. They breed CO and/or CAO and they are serious breeders, they have a web page under such name; Daur Don and Talisman are part of this association. Good luck with your research. hugo