You can purchase plexiglass by the sheet at any of your local big box hardware stores. Home Depot and Lowe's always have plexiglass in stock and you can buy by the sheet or have it cut for you. Some Ace Hardware stores can order plexiglass for you, but they may charge you for a special order. In most cases, you may be able to find the best deals on the internet. But, Home Depot and Lowe's are the two best places to start.