Couldn't you just call the following replaceing the {zipcode} with the zip code or city and state
http://maps.googleapis.com/maps/api/geocode/json?address={zipcode}

Google Geocoding

Here is a link with a How To Geocode using JavaScript: Geocode walk-thru. If you need the specific lat/lng numbers call geometry.location.lat() or geometry.location.lng() (API for google.maps.LatLng class)

EXAMPLE to get lat/lng:

    var lat = '';

    var lng = '';

    var address = {zipcode} or {city and state};

    geocoder.geocode( { 'address': address}, function(results, status) {

      if (status == google.maps.GeocoderStatus.OK) {

         lat = results[0].geometry.location.lat();

         lng = results[0].geometry.location.lng();

        });

      } else {

        alert(Geocode was not successful for the following reason:  + status);

      }

    });

    alert('Latitude: ' + lat + ' Logitude: ' + lng);