I eventually found a supplier in Germany. However, they had sold out! Towards the end of the year I got a plant through the post from them, the last they had, and then discovered that they are a regular visitor to plant fairs in Italy
www.uhlig-kakteen.de The plant survived the damp and, at times, extremely cold winter and is now just coming into flower. It is a slow grower. Very little noticeable difference in size from last year. It is evergreen so what little growth it does make is not lost. I shall try to get leaf cuttings on the go because, if I were to lose it , I am sure it would be difficult to find again.