HI Karel,
Check my website: http:
www.brucecorwin.com and go to the montana pages. I would recommend just going to the West Yellowstone area. That will give you access to more water than you can fish in a month. Tons of wade fishing all over the place. The Firehole, Gibbon, Yellowstone, Madison (in the park), Obsidian Creek, Iron Stone Creek, and on and on. Plus you're in and around Yellowstone. If you've never been there, that's worth the trip alone. You can find tons of motel lodging there. We rented a house near Blue Ribbon Flies. 4 guys for the week cost us about 180.00 each.
Best,
Bruce