This is undoubtably the hardest trophy of all to kill now in Idaho. I have only seen a couple over the last 5 years, and not when I had a rifle handy. I find tracks all around my bear hunting area outside Idaho Falls, but have yet to see one there.
Unit 61 up in Island Park area probably has the most, especially since it borders Yellowstone Natl Park. Beautiful area and the fishing is good up there!
My friends have killed 5 in the past few years during the Sept. archery elk season around Sawtelle Mt. One of my security guards out at work actually killed TWO with his bow in that same unit. The other areas to consider would be down around Salmon and the river corridor (30/28/21/21A), or up towards Challis in Units 36/36A/37/37A. I don't have any experiences to offer for any of the areas further North.
Are you coming out bear hunting? Remember that a deer tag in the Fall may be swapped/used for a bear, lion, or wolf. Good luck.