They're on ebay. It looks like they come in three flavors right now:
$359 - Fully populated - Item number: 270789723839
$290 - Valves - Item number: 270789726680
$249 - Bare Head - Item number: 350564478176
Member of the Dropped Valve Seat Club.
Replaced #4 Piston, Rings, Rod+Bearings, AERA Re-Manufactured Cylinder Head and a light Hone. Then CLEANED the hell out of everything.