the blade is a standard rover maestro type , available from most key cutters for a couple of quid , but the shaped bit of plastic you need on the disco blade so it snaps into place within the fob is obviously not on the maestro one. blades with the special shaped bit of plastic are available...

there are pattern parts available which are a bit cheaper : http://www.paddockspares.com/products.asp?category=DISCOVERY%202%20(1998-2004)&subcategory=Suspension&product=Rear%20Air%20Spring%20-%20with%20self%20levelling%20supsension%20(WEB%20EXCLUSIVE%20SPECIAL%20OFFER)

You are right about the towing electrics plug behind the offside light cluster , it just needs the protective cap removing. You dont have to remove any trim the wires can be fed from the plug to the towbar , follow the wires for the indicators as a guide.