I'm a 'tourer' so no expert on statics, but yours is a subject that crops up often enough, and the general response is 'no' or 'as rare as hens teeth'!
Sites like to profit from the sale of a van to you from their own stock/agency, and likewise buying your unwanted van from you at a huge discount, so they by and large won't allow 'bring ons' or 'off site sales', all in the T and Cs!
I have responded to similar posts many times, and the answer is you would be more likely to find a flying warthog. Very few site will allow this anywhere in Britain, let alone in any specific area, it's simply not in their interest. I usually conclude by asking the poster to let us know if they do find one as it could help others in a similar position, but as yet I haven't had anyone come back with a response.