Go here:
http://www.gwagen.com/
My understanding as to why there are very few G-Wagens in the the US is because Mercedes-Benz of North America (now MBUSA) has always refused to sell and service them. Europa International has been the only authorized imported in the US for years. They have been trying to knit together a network of dealers and service centers. Benzmac talked to them last year about being a sales/service outlet. If there's demand, MB Autowerks may do something along these lines.
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Bill Wood - Webmaster
MercedesShop.com, LLC
MB Autowerks Inc