I don't know how useful this idea will be...but here goes! Have you thought of getting an older dog from an animal refuge or a rescue organization? But only consider a dog whose past history is known & who has been observed for some time interacting with the other animals. For example, a particular dog might have come from a background where it lived peacefully with other animals, including rabbits. Or the dog might have interacted peacefully with rabbits while staying at the refuge/rescue facility.