I used to make a living in the chaga business and funny enough, was Mt. Rose's main supplier for a number of years. They were great people to work with. It's been several years now since my business has been active, but I do consider starting it back up from time to time. My main picking grounds were the Upper Peninsula of MI, and I would buy chaga from WI and MN to resell as well. As far as medical benefits, I think there is a lot of hype and probably some truth to all the claims, but it's hard to figure out which is which. One reason I stepped away is from all the people emailing asking for medical advice, or clearly putting all their hope in this fungi that could well turn out to be 'snake oil' for all I really knew; that will weigh on you after a while.
You may be able to find the odd chaga conk up in the mountains of OR. I've heard of it growing in the Cascades anyway.