Hi.
If it is a white diffuser (not reflector), it can be salvaged from a defunct lcd monitor or tv and cut to dimensions. If it is the topmost polarizer film, same solution but needs very skilled hands and total cleanliness to peel, cut and re-apply. If it is a silver true reflector, try same source. I probably have several of each in my parts bins.
Anyway, to replace those films, it has to be dismantled. If you are there already, try cleaning the 'clouds' with some other fluid, perhaps alcohol.