Where can i buy the metal track like you see at all reptile shops where two pieces of glass slide sideways.?

Actually, you can buy these types of terrariums already made!  They are not extreamly cheap though unfortunately!  Big Apple Pet Supply have a Pro Serries Granite Acrylic  Cage with Sliding doors!
specifics:
Sliding Glass Doors on professional rolling tracks are the entry point to these beautiful granite acrylic reptile enclosures. Our pro series acrylic reptile cages are ideal for most species of reptiles and amphibians as they are moisture, odor, stain and scratch resistant. In addition, our pro series cages come with a solid screen top to allow any type of lighting or heating system to be utilized. Of course, We will be happy to provide you with a free full consultation on choosing the perfect enclosure, including the correct heating, lighting, substrate and accessories... creating a beautiful and healthy environment for your pet.


If that is too expensive, That Pet Place has a terrarium with front opening glass which starts at $64.99
specifics:
Treat your reptiles and amphibians to a home specifically designed for their unique needs. Unlike a standard aquarium, this glass terrarium features front-opening doors and a removable top screen for easy feeding and maintenance. Unique front-window ventilation is ideal for arboreal species like chameleons. Adding accessories is simple with the raised bottom and 10 wire and tube inlets. The system also holds water up to its doors, making it excellent for semi-aquatic species. Includes a unique, rock-like background for creating the ideal realistic habitat