A couple of weeks ago I stumbled across a toy theatre shop in Covent Garden, London. I say stumbled but it's been there since 1880.
Benjamin Pollock's Toy Shop
I had to buy something, so I eventually decided upon this cardboard diorama peep show.
Just need to work on my cutting skills before I attempt to put the thing together myself.
One idea would be to use this as a template to make my own.