Sorry not sure abouut ex-mod but you could try Tek Tanks, there web address is something like :-
or put in Tek Tanks in your search engine. They are in the UK.
They can offer a standard tank up to 90 litres or they can make custom made fuel tanks, you need to send them drawings and allow a 5 week lead time.
Their telephone number is 01420 520830. Sorry know its not exactly what you want but it may be a plan (b)?
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