Pacino wore a black Homburg by Cavanaugh in several pivotal scenes, including the one in which, for the first time, he has started to look like the new Don Corleone (when he walks down the street with Kay, shadowed by his car, after having returned from hiding in Sicily).
This particular hat was auctioned by Profiles in History in December 2005. You can read more about it here:
When you open the page above, go to the PDF files for "Auction 23" (the cover with Earth vs. the Flying Saucers on it) and download the third file (lots 243 to 398). You'll find the hat and text on Page 109 (Lot #268).
If you haven't already, you might sign up for the Profiles in History mailing list. They send out announcements when a new auction is coming up. That announcement is accompanied by the publication of a new catalog, which you can download from their catalog page (linked above. Bound copies are available, too, for a price). You'll also need to go through a (free) registration process in order to bid on live auctions.
Then you'll be set to chase items from The Godfather that might become available in the future. :love