I just typed "Rover 45 cruise" into the search function on eBay and this immediately caught my eye:
http://www.ebay.co.uk/itm/Land-Rover...item43a686404e
Discovery TD5's from 03 on should be pretty plentiful, and the switches pictured look suspiciously similar to the ones you find controlling the radios on R45's. TC, have you investigated this route already?