Desperately need to know if roof vents smaller than 280mm X 280mm exist!!!

I'm doing a trailer conversion, but to be able to realistically have a kitchen installed I need ventilation. However, the space available on the roof that I can cut out is pretty small and 280x280 would be too tight. Does anyone know of somewhere I can get one smaller?
For reference, I am after something like this: http://ift.tt/1STkCor

Submitted April 08, 2016 at 02:07AM by ElExtraMass http://ift.tt/1VBHdIw