Anyone know the best or a good site to purchase a windmill to provide electricity for a single private home?A portable one would be better but any will do.

Have you checked the farm and feed stores in your area? If you have any in your area. Otherwise look online or in your yellow pages.

Here are some online sources:
American Windmills Home Page
Windmill Plans     www.fuelless.com
Brasada Windmills - Aermotor Windmills with Wood or Steel Towers

Here are couple of additional sites for portable units:

Agriculture equipment, farm magazines, farm equipment, farm inventions, farm machinery, agriculture machinery

WING - The Portable Windmill | GeekAlerts

Do a web search for "portable windmill".