Quattro Farms (which appears in the Union Square Greenmarket here in Manhattan every Saturday) does geese and would probably be able to get you goose fat. They are on Route 44 in Pleasant Valley, NY 12569 1-914-635-8202. I think their geese run about 3.95/lb.
Last time I was in the store, Balducci's (the original store, on Sixth Avenue at 9th Street) was selling goose fat in pint tubs. 212-673-2600, ext. 3418 (butcher)