You can find these very useful accessories in fireplace specialty stores or even some hardware stores and big box home centers as well. A search done on your favorite search engine will provide information on where you can purchase them as well. You can even buy them online but keep in mind that you will pay shipping and handling charges as well.
A fireplace glass door is installed on a fireplace to keep the room warm longer when the flames die down. Whether a wood burning fireplace or a gas burning fireplace, heat radiated into the room escapes through the chimney. One does not notice this while the fire is burning brightly, because of the heat from the flames that radiates into the room. However, when the fire starts to die down, the hearth becomes cold quickly as the heat escapes through the fireplace opening. To stop this from happening, a fireplace glass doors blocks the opening, keeping the warm air from leaving the room.