Bad news, I hope you find one locally. From bitter personal experience with other cars in the past, DON'T be tempted to buy with courier service of body panels, despite the best efforts of the seller to bubble-wrap etc it's no better than a 50/50 chance that it arrives un-dented once the courier chimps have lobbed it about!
Thank you for the replies chaps, based in London but willing to travel. I know that I will need to collect as thin gauge steel and DHL chimps don't go well together.
Check out classiccarspares on ebay. He usually delivers / posts stuff to you rather than having to fetch it. The one below needs a little tlc but if you contact him he may have others?
http://m.ebay.co.uk/itm/BMW-Z4-E85-E86-DOOR-PANEL-LEFT-SIDE-STERLING-GREY-/262948761939?hash=item3d38f7b153%3Ag%3ALR8AAOSwzqFY-7e3&_trkparms=pageci%253A38aee2a6-2ab2-11e7-8481-74dbd180966c%257Cparentrq%253Aaba0492415b0a9cb1be5d5cbfffe97ac%257Ciid%253A5