Welcome to the Cake Decorators Q&A

Where can I order one of the large green board that is used in the videos on the work space for fondant?

Try here: https://www.surbitonart.co.uk/cake-boards-and-boxes/non-stick-boards/non-stick-boards-1.html
…… and here: https://www.cakeflix.com/questions?s=green+board

I bought mine from Surbiton sugarcraft shop because at that time they were the only people who had the largest size and they were the cheapest. Times have moved on, it’s best to shop around online for better prices. Google ‘ large nonstick workboard for sugarcraft’. If you are not based in the UK, please search on Amazon or ebay.
Good luck with your search.