The US has several companies that deal in UH-1H's as well as parts. We deal with them all of the time with reference to conducting certification tests. All of my flight time in the past 6 years has been with UH-1H's modified withe the PT6C-67D and a Tail Rotor Enhancement Kit.
As far as other versions of the Huey are concerned, there are few UH-1B's through P's. Only one UH-1A as far as I know. Uh-1H's can be bought and I know two individuals who can sell you one.
As far as certification is concerned, ex US military aircrfat can only be certified in the Restricted Category -- no passengers for hire. Can use for Ag work, sling loads, etc. Bell 205\'s and 204\'s can be used for Transport of paying passengers and since they are not in production, they demand a premium price.
I am working with a well-to-do individual who has a UH-1H for grins and it will be in Experimental, whwn ready for flight.