Lots of good deer in SD. I've got an uncle that built a cabin on the banks of Lake Oahe and we go up that way to shoot pheasants. I've seen some real monsters. Don't know much about the area you're talking about but the people in SD are really friendly for the most part and are pretty good about letting you hunt. I'd go out to where your tag is and start knocking on doors. Let them know you are military and I'm betting someone will let you on. You could also stop and talk to the local sheriff. They know everybody and could probably direct you to the right landowners. Many of those little towns also have a VFW Hall. Drop in, have a beer and introduce yourself.

Good luck.