It's been at least 40 years since I've seen either a Greater Prairie Chicken, or a Ptarmigan - saw both in mid & northern Saskatchewan, but haven't been back there since.
I understand populations of these birds have become sparser in their Canadian habitats as the years have passed, but I expect you could still spot some in the Prairies of our country - summer/fall for the Prairie Chicken, to winter for Ptarmigan.
Have no idea where you'd find Ptarmigan in the U.S. - perhaps northern Minnesota - parts of Michigan - perhaps the Dakotas. As for Prairie chicken, maybe the grain fields of areas like Wisconsin & surrounding states ?