AE Wilcox had a load of them last year, but he was not then willing to sell them except as part of a complete system. He may have other thoughts on that now though. Worth a try on 01454294465 or 01454294213 ask for John Wilcox.
(Part numbers are Manual: WCD001791 & WCD001811, Auto: WCD001950 & WCD001960.)
David