its difficult to tell from the pictures mate.
you would really need to remove one side of the face panel and take a picture of the actual tensioning system to identify what one it is.
you can see a groove/recess running down the side of the box. in that groove you will find a row of small screws. if you remove them it will expose the tensioning system. take a picture and post it in this thread.
its not just a case of a banner. the banner material needs to be the right one, the right size and also made to accommodate the tensioning system being used. some are simple folds in the skin and clamped, others have rods running down a pocket in the banner which is gripped my spring loaded hooks and so on, there are a good few out there these days… once you identify the system, ide give the order to the manufacturer to have the skin made properly to your size/spec.