Search for Mityvac my friend, there is a specialist place in the midlands (if I remember) that does the spares as well.
I got mine from Hein Gericke - £36.99 item no 29000341
http://www.hein-gericke.com/hg-shop/...b_frameset.php found the other supplier as well:
http://www.premiertools.co.uk/item2140.htm - a bit cheaper.
Frank