Unusual sized roof light

[Sydney1]

I need to replace the rooflight on our crossover bay. It was imported from Australia and I believe is a Sopru conversion. The opening is 400mm long x 300mm wide and because of the shape of the roof moulding the maximum width is 500mm. I can't seem to find a direct replacement so before I look at a compromise solution anyone have any ideas for suppliers of unusual size rooflights. I think I've tried most of the obvious ones.

Thanks