Matt, you've actually got an excellent resource right there in Austin, in the form of Ebay's "Lamont Sanford", aka Larry Chabira.
He wheels and deals in lots of Airhead and Guzzi parts, and has had several used engines for sale of late. He's also completely trustworthy, and a great source of info too.
You should be able to email him at lamontsanford@sbcglobal.net.
Of course there are other sources too, but I'd definitely give the local guy 1st shot, for convenience sake and shipping costs too if nothing else!
Good luck! [smiley=thumbsup.gif]