the v12 throttle cable is a specialised item that has a special bracket in the engine bay for the kick-down microswitch , the cable also has a cam built into it at this end to operate the kick-down microswitch
these are, as you have found out NLA from Jaguar or anywhere else as far as i know , i did manage to buy a brand new one several years ago , but have not seen one since,
just to make you aware, a throttle cable from any other jaguar v12 or no , will not fit , for kick-down reasons ,
pm me if interested in a very good condition used one ,
BB