Lots and lots of farms have 400-600 amp service. Even unused farms, tiny little double wides on 10+ acres are common in south Jersey, and all of the outbuildings are powered, I usually see these elaborate rigs in the boondocks too. And anyone with a dock on a serious piece of water probably has 3-phase 440v, 500amp running to the shore power outlet.
Second hand diesel generators (think of what a commercial building or small data center would use for backup power) are also not that hard to come by.