Hi, I visited Phoenix Engineering in Slough yesterday to collect a set pf replacement shells for my N type. I spent many years working as an engineer in engine manufacture so asked for a walk around their shop. I thought them well equipped for small batch production and very competent and knowledgeable. They know all about MMM cranks as well as those for many other pre war engines. You can buy from them directly or Peter Green may have one in stock. Best regards, Chris.