The person to get ahold of is Steve Yonce. He is over the GIS department Manager for NorthWestern Energy. If he does not help you, call Jim Trolia in Butte. If you just call the main NWE phone # - they will transfer you to your desired party.
P.S. Welcome to MAGIP!!
Hi David - You can also touch base with Tom Ring at the Montana Department of Environmental Quality. Tom manages utility location for DEQ and has an extensive collection of existing corridors some of which is available to the public.