When you turn onto 136, just past the driveway to the Visitor Center is the kiosk (you can see it Google Earth just past the driveway, and right on the side of the road). The first time I found it was after dark, and I didn't have any issues. I think they might include some pictures on their website/form that show the location, but I can't swear to that as it's been a couple of years!
