When your going through Miles City stop in at the Region 7 Wildlife office. You will walk into a room with about 6 to 8 people in it who will put you into what ever type of game you want to hunt. Depending on the Block Mgmt. they can even give you the written permission you need right there. Or they will give you all the contact info you will need to contact the land owners but as stated earlier most of the land owners are booked solid, you need to do this in August when the BMU are put out for that year.
Also which worked for me I was in Broadus looking for Sage Hens to get mounted. I went into Powder River Taxidermy, told them what I was looking for and I told them that if I got the birds they would get my business. It was a win win situation for both of us.
Good Luck, I would not go that far for a deer but I would for a bird. but then I have feathers on the brain.