Tom, To raise & lower my inverted V antenna I'm using a cheap (possibly polypropylene I think) builders chalk line, a 30 Mtr length for about £1.29 from B & Q (maybe cheaper at a builders merchant),
Try Boat Jumbles. (Chichester has one early Sept) but they are all around coast often in aid of Life-boat funds. "Yachties" discard running rigging at the slightes hint of obselescence (ok ok I cant