Hi Teifion, have you tried the Register's sales? They might have one :)
looks like they haven't :(
they appear on ebay from time to time though
Colin Murrell PA0786 (D0285 previously) Photographer for MGCC (LeMans Classic, Oldtimer Grand Prix etc) & MG Motor (BTCC 2012-5) http://www.triple-mracing.com/