I know of the breeder and Dam mentioned above.
Before you choose a breeder please think about what kind of activites you would like to get involved in as not all breeders are producing dogs that can "work" in any particular venue. If you buy a dog as a "pet" and then decide you want to get involved in agility or obedience you may come into some difficulty, especially if that dog has no titles in any particular venue in it's pedigree. Locally, many breeders tend to be producing for conformation ONLY and I'd like a dog with beauty AND Brains.
As for trainers, I could recomend Lietash Training Academy,
Lietash Canine Academy - Training, Dog Sports, Boarding, Fun with your Dogs I know them through Flyball. They don't spcialise in rotties but they have been around for YEARS and as people involved in with Border collies, Jack Russell Terriers and rescue work, I do believe they have seen and dealt with a lot of different breeds and different behaviours. They have always been very nice to me when I've had difficulty with Bear at flyball and we LOVE going to their tournaments when we get a chance.