I've never done business with them, but I happened across BritishCarKeys.com a few years ago when looking to get copies of my door keys (the non-anti-burst ones which are different than the ignition) and the numbers stamped on mine were in the range that they could produce. I'm not sure whether they can do ignition keys (mine doesn't have a number stamped on it) or whether a record correlating VIN number to ignition key number still remains for Series Rovers, but they might be worth reaching out to for advice on tracking such a thing down.