The generators are privately-funded and privately-owned, according to a marathon spokesman quoted by the Post:
The New York Road Runners Club, which organizes the world-famous race, is paying for the generators, which were supplied by Long Island-based On Site Energy for the massive, 80-yard-long tent.
http://twitchy.com/2012/11/02/backlash-against-nyc-marathon-intensifies/
I guess the question then would be whether others—such as the City itself—have tried to rent more local generators but been turned down because there aren’t any more available.
And if not, why not?
You know fully well that power utilities are not 'private' in any meaningful sense as, say, Macy's is private. Does Macy's get its income from taxes and fees government levies on the public? Regardless, all utility-owned generators in the area would normally be put to use helping residents during a disaster. Requisitioning them for the mayor's preening display is not acceptable.