Stuart:
Don't know on what part of the world you are located but there are some small commercial operations that have experience with and build steam powered electrical generating systems.
Mike Brown (located in the USA) at
http://www.mikebrownsolutions.com/mbsteam.htm
started with the "great Millennium scare" in about 1997. He has a couple of small plants, but in recent years has developed a 20HP engine. I have heard conflicting reports about his integrity but have no firsthand knowledge
Rod Muller at Strath Steam (located in Australia) at
http://www.strathsteam.com/
started in on marine, but became sidetracked by a demand for electrical generating systems needed by "stations" (ranches) in the Australian outback. He's been doing it for over 20 years and, while I've never seen his gen sets, I have operated and installed his engines. I have the highest regard for their good engineering and quality construction.
There are several others around. You might look at the links pages of some steamboating websites such as the International Steamboat Society at
http://www.steamboating.org as many steamboat engines will satisfy your needs. I personally believe that a marine two cylinder, high speed vertical would be best suited and probably readily available. Strath Steam can supply your needs best in that area.
Sorry, Edward, that those of you in the homeland have lost this precious independence, but us colonials will carry on. :P