thanks for that posting, I took a drive out to Burloak today, bumped into a couple of other birders and we saw all three species, although I didn't count a hundred - closer to fifty. Here's where we saw the Snow Buntings and Lapland Longspurs:
http://goo.gl/maps/bwNA (look for the green arrow on the map). They let us get nice and close, we had some great views.
The Horned Larks were bombing around in the same field, apparently picking fights with each other. Also flushed a couple of Killdeers across the road. We just parked on the west side of Great Lakes Blvd. and crossed the road at the lights.