If you're near Wenceslas Square there is Foto Skoda, and 100m metre down is Jan Pazdera; two of the larger antique camera shops in Prague. No Leica's to be had, but a lot of interesting interesting folders. I bought Tri-X from Foto Skoda before.
Another 400m down from Jan Pazdera is the Leica Gallery + Cafe.
Another 400m down from Jan Pazdera is the Leica Gallery + Cafe.