In reply to Ben_Climber: You can zoom in and print maps off from this site:
https://map.schweizmobil.ch/?lang=en&bgLayer=pk&resolution=20&X...
Otherwise, as others say, you'll have no problems buying maps over there, 1:25,000 or 1:50,000.
The 'Landeskarte der Schweiz' 1:50,000 for the Eiger region is number 5004: "Berner Oberland", this has Interlaken at top centre, Eiger, Monch, Jungfrau in the mid centre, so it covers a large and very interesting area.