I had mine knocked off by another driver a couple of months ago. I got a replacement off ebay. New but not original Ford. Go to ebay and type 291116906849 into the search box. That will take you to a passenger side, heated, electric mirror. Its the same seller I bought from. Cost £37. Its not quite the quality of the original in that the pivot point is not as tight but the cost is reasonable. The cover on the one I mentioned is primed but it unclips easily so you can either spray it with a spray can or maybe use the original cover if its in good nick.
I lost mine on the way to work and ordered at about 11am. It arrived at 8am the next morning. Not bad for free postage.
You need to pop off the little speaker trim first to give you access to the other screws. ISTR one of the screws is well hidden so be patient and don't try and wrench anything off.