What I did, is go to various car sites (cars.com, edmunds.com, and drivechicago.com) and submit a request for quote from various dealers. I also found all the GMC dealers in the Chicago area and went to their sites on an almost daily basis. As soon as I saw a Terrain that I was interested in, I would email the dealer.
I ended up getting lucky. Found the model I wanted on a Saturday at Marqhardt in Barrington. Any luckily it was still there on Monday when I went back to buy it.