There is a chaga mushroom brand from minnesota, (its a small company). If cold temps do infact make better chaga (?), these probably are be the coldest exposed Birch grown chaga in the lower 48 states.
Their website is partially complete, the bag label says "Up North Organics"
www.minnesotachaga.com/buy-chaga.html"Our Chaga is harvested from Northern Minnesota Birch trees. Because harsh weather conditions (think -40 degrees) are known to provide a more potent Chaga, Minnesota Chaga is especially sought after.
Minnesota Chaga
3 oz Ground Chaga $8.99
(makes 7 gallons) +$2.00 shipping"