I used two different types. One can be found at Murrays:
http://www.murrays.com/archive/50.pdf (see "B") but you have to also order the fairlead. It is actually jut a strip of metal that attaches to the pin on the bottom of the drum and it has a hole near the top to guide the furling line into the drum. Murray's probably doesn't stock them, but I can get you a picture.

The other one you would have to special order from Murrays or any other Harken dealer: http://harkenstore.com/uniface.urd/scpdinw1.ShowProd?B4RPMEB9Y9AV34

I wouldn't use the TheMightyHobie18 furler because it is a below-bridle furler and would be difficult to mount correctly.