Did you try searching by part number?
I think this is it, but it's hard to tell from the schematic
137-18547-00-00
http://www.nwvintagecycleparts.com/search-results.php?q=137-18547-00-00&st=spart&search.x=19&search.y=13
This guy charges a lot for shipping, but basically overnights it. I would...