Thanks for the link.Lastolite do a kit that contains one: here
not sure if they sell it separately though.
Yeah thats my last resort, i want to avoid the shipping costs if i can.I don't know if it helps, but they offer international shipping.
Have you tried Ebay? This one's in Hong Kong but shipping costs seems reasonable.
http://cgi.ebay.co.uk/Diffuser-Umbr...ryZ48515QQssPageNameZWDVWQQrdZ1QQcmdZViewItem