Seems like you can always find an F2 or two in the back boneyard of a friendly Allis dealer, but if not...  I found 2 for the gas engine, and based on the amount of parts these guys have, I'd imagine they've either got it or can get it.  Fairly reasonable considering.  Their 1-800 number is on the website.  http:__www.abilenemachine.com_combine.html