In Orange and Putnam counties, there are a bunch of horse farms, which could make for good groundhog spots. The horse farms seem to be on smaller acreage though, so tougher to hunt.
I've been emailing and calling farms within 2 hours of NYC with limited success so far. Knocking on doors might be more effective, if I can find the time. I might also try further north.
Do you all just drive around and look for burrows in fields then drive up to the house and ask for permission?
Certainly PM me if you'd like to share favorite spots.