With the new 5135-ship, the front riggings are back in these colours, but the ones for the aftmast are shorter on the 5135 then those on the 3550/3750 pirates' ships, so no chance of getting a spare from DS...
I've no spares for the 3550 left, but if I were you I'd ask around here or look on ebay or so for this specific rigging. You could also look for flagpoles (masttops) from the 3750, the 3940 or the 5135 to put on the top of the ship's masts.
Or do you want to keep that ship like it is?