Where can i find 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.