You can't teach just any horse to gait. If you could there would be a lot of cowboys riding fenceline on guarter horses that gaited. (Althouth there is something called an Indian Shuffle that crops up in quarter, apps and paint horses every once in awhile. It's basically a smooth running walk and highly prized.)
You can also take a young horse, and by faulty riding, wreck his gait. A lot of heavy people buy gaited horses because they assume it's easier. They don't have to post. What they find out is that unless the horse is built like a total tank, he ends up pacing. You do NOT want a horse that paces. Envision yourself in a blender...that's what it feels like.
So try a lot of horses...more than one from each breed and take your time. Look outside Virginia. Gaited horses are going to be more expensive in areas where they are scarce and less expensive where they are common. It only makes sense. Also, most areas of the country are still reeling from the downturn in the economy and people are looking to get out from under the expense of a horse. A good horse is a good horse whether you buy him from a gaited farm, or an individual owner. What is most important is that you have someone near you who knows what they are doing and is willing to help you if you run into problems.
Take your time. There are a lot of gaits out there and a lot of horses.