I contacted s2000 before i bought mine, had loads on the webpage and also pistonheads and a few on ebay, When i phoned the bloke (steve) he said they didnt have any in stock as they were all being sold online but he was getting one in the week after and if i gave him a 250 pound deposit he would hold it for me...he sounded very dodgy! I dont know how he gets away with it.
Norman motors in poole have a nice soft top in on a 2006 very tidy but over priced but you do get a gold warranty from them and they will even source one for you, bought my last four cars from them and been very happy