I took Smurf there once to show him as he used to work in a caravan fitters and had worked on many Commers back in the day. Anyway he looked at Smurfs roof light/vent and pointed out it was an odd large size and he had a brand new old stock one that had been sitting around for years.....I didn't buy it so he may still have it.....well worth a try???
Just out of interest he had kept up untill about 2 years ago an original mould for making the fibreglass roof that was exactly the same as Smurfs...