A Chevrolet 2500 can be bought directly from the Chevrolet company website. In addition, many dealers also carry the Chevrolet 2500. Also, classified sections on popular websites such as craigslist regularly sell cars.
There are many certified dealers in the US where you can shop for a BMW. These dealerships should be able to answer any questions that you might have concerning performance, safety features. Many BMW dealers have a wide range of models that you may be wanting to purchase.
New Chevy trucks can be purchased at Chevrolet dealers throughout the United States. These dealerships can be located by checking the local white pages. Many of these dealers also advertise their locations in local newspapers.
Motortrend and the Chevrolet website both give locations of dealers in whatever local area is searched. A new Silverado can be found at a variety of dealers in each area. Used would be a little more specific of a search.
Yellowpages and Yelp are good sites to find new auto dealers in Houston. They have lists of the dealers and customer ratings to allow one to choose the best. Some the dealers are 'Fred Haas Toyota World', 'Paragon Auto Transport' and 'Lone Star Chevrolet'.