Tom,
All the good the Fly Shops in the Montana, have River Access Maps of all the big rivers. The publisher is River Rat Maps and believe me, the $5.00 it costs is money well worth spent!
The Upper Madison between Quake Lake and Ennis has an abundance of easy, access points for wade fishing. To start with, there is Bridge #1 & #2 at Reynolds Pass, Three Dollar Bridge, Pine Butte, Eagle Nest (My personal favorite) and close to the town of Ennis is Valley Garden as well, just to name a few.
Mariekie