Two national retailers will be making their debut in the Buffalo Niagara region and each will be opening within a short distance from the other. Dover Saddlery, the Wellesley, Mass.-based equine-based chain, will be opening its first Upstate location by early summer, with the retailer leasing 7,000-square-feet in the Premier Place Plaza on Transit Road in Amherst. Founded in 1975, Dover specializes in everything from riding apparel to saddles and other types of equipment and merchandise for horses…