Unfortunately, the original to this is hard to locate. It was distributed by the AMS at the time of the colloqium lectures, but they apparently didn't keep the files they used. At one time it was distributed as a Geometry Center preprint, but the Geometry Center is now defunct. I've lost track of the source files through multiple moves, computer crashes, etc.
What I have is a scanned version of the Geometry Center version that is legible but not beautiful, which I can forward by email
Bill Thurston
ADDENDUM: Renaud Dreyer told me of an online scanned version I wasn't aware of, which appears to be better quality than the one I have:
