I was about to suggest writing to Ground Force, but I just found out that they no longer accept requests. Perhaps there will be other gardening shows in the future. I'll have a look around.
I thought for ground force and the like you had to pay? What about Carol Vordermans better homes? Or approach you local garden centre and say in return for you giving them free advertising and letting other people see it [the downside] they can do it up for nothing? remember thho' there's no such thing as a free lunch - you might not get a choice on what it looks like!