Large hardware store chains such as HomeDepot.com and Lowes.com sell track kits for sliding doors. These kits are available in various sizes to match specific door dimensions. Individual parts are often available separately as well.
The track kits come in variations for sliding by-pass doors, hanging sliding doors, accordion doors and more. Knowing the exact door type and size is essential in selecting the correct track kit. Full kits include mounting and installation instructions.
Both of the previously mentioned retailers sell complete sliding door sets. These sets include the doors, all the hardware required for installation and a set of instructions.