ANYONE can purchase a Federally Documented Vessel in the United States but only American citizens can continue to keep it reistered that way.
I personally know several different Alien Life-Forms who have come to the US Virgin Islands and purchased American built & documented yachts. The buyer and seller (or broker) simply drive to the airport office of the DPNR together, sign a form, pay a few bucks and walk out with new registration & title in hand. People from Puerto Rico come over here to register their boats because it's so easy... and cheap.
Furthermore - it is my understanding that, due to the free trade agreement between Australia and the United States, there is no longer import duty applied when bringing a US made vessel into Australia. Just be sure to bring documentation showing the vessel was built in the US or made with US supplied materials.
Plenty of boats for sale around here.
A great resource is
Boat and Yacht Sales, Buy Boats and Yachts - YachtWorld.com for comparison shopping.
Happy Hunting,
Kirk