Grand Slam tennis champ Michael Chang won't rest on his laurels after retiring from the game this year. Along with brother/coach Carl, he is acquiring Denver-based Dunton Realty Co., a 100-year-old retail brokerage and property management firm specializing in neighborhood centers. Chang's holding company, CMCB, has invested in several commercial properties in California, Texas, Arizona and Colorado in past years. With the Dunton acquisition, the Changs are ramping up development of new centers, anchored by tenants such as Kohl's and Albertson's.