Thanks Jack and Dale,
I thought I woud try the forum first; there are new re-manufactured ones around from various sources. NOS are quite difficult to get hold of but Mk 1 Cortina ones are quite easy to get hold of but not the same as the Mk 2.
Looking at the Austin Healey type, its quite different Dale, although it may have the same bore.
Anyway, eventually sourced one from Burton's.