These might get you pointed in the right direction.... http://kmsha.com/ http://www.rmhorse.com/index.php http://unitedmountainhorse.com/home/
And if you google or you tube RMH/KMH videos there quite a few that show and explain the different gaits thay can do. These in turn can direct you to various breeder websites that also have informative videos.
Like Tennesse Walkers, Missouri Fox Trotters, and other gaited breeds, KMH/RMH can be incredibly smooth and a joy to ride.
As for being a good beginner horse, well much depends on the horse's temperment.
Something to keep in mind is if you ever intend tolearn to ride non-gaited breeds, they are bit different and you will need to develope a seat for them as well as the gaited horse movement.
There are also some good forums out there dedicated just to gaited breeds that can be easily googled.
Happy info hunting.