For Zermatt, best walking map is the Kummerley and Frey Visp-Zermatt Walking Map. Also the BfL ski map if you're intending to use the alpine paths in the high mountains. Can probably get these from Stanfords. Contact Zermatt tourist office http://www.zermatt.ch for free overview maps and suggested walks.
Stresa, no idea, but try Stanfords.
