Try Dave Kelly car breakers they are in Wrexham, he had 3 a few months ago and one was in a Marina Van, has bigger servo. Give him a call 01978 843253. He is primarily a jag breaker so may be good source for those bits. i got G/box, propshaft from him and handbrake (Xjs).
I got my Marina pedal box by using a broker for used car parts i think it was www.1stchoiceonline.co.uk they advertised in Thompson directory hope that helps