ebay is an option. one on this link
ebay mast. Ebay in the states is cheaper, got mine from over there for about half the price including shipping.
I did a walk through on this thread
clicky if the white toothed cord has broken off inside the antenna mototr unit, just in case yours has done this. Although yours is a Mk2 and mine is a Mk1, the setup will be very similar if not the same.