I'd have to say rarely, but they aren't that hard to hunt.
I've harvested 6 in 30 plus years of hunting them. There have been a lot of years I passed on harvesting one. Many times I'd find some in a drainage that would kill man, or horse to get it out before it goes bad. Some places I'd have had to set down with a knife and fork to get any of it out. Two weeks ago I was in the dark timber an hour before daylight waiting for the elk. Right at shooting light a group of rag horns and cows were walking to me. Unlucky for me, but lucky for him, another hunter who had come up behind me saw them cross the saddle and he got a nice cow out of the bunch. Well, that spooked them pretty good and they went by me I'd guess pretty close to full speed. I couldn't put the sight on a piece of hide.
Then down below me one of the 4-5 pointers stopped in some trees at about 60 yards. There was a 12" tree he was standing behind, but I could see through the branches his shoulder was right at the edge of the tree, but the brush was to thick. on the other side of the tree I could see the whole hind quarter. I looked at a spine shot, right at the back of the liver, to chancy for me.
Maybe I'll find him next weekend for my daughter. She's got a bull license, but I'll be hunting cows. We'll be up there hunting though, and that's why I do it.