I-70 to Georgetown, then follow Guanella Pass road to the top. In winter, they usually close the road a couple of miles from the top. Extra snowshoeing/hiking required.
I usually snowshoe until I find their tracks, then follow the tracks until I find the birds. I find it best to lie in the snow until the birds get used to you. Plus you get more intimate portraits.
Winter is a great time to photograph these birds. Their winter plumage, combined with some fresh snow, makes for some clean images.