If you are missing cs_italy.bsp, here's what I would do:
Step 1: Open Steam
Step 2: Go to your Steam library
Step 3: Go down to where it says Counter-Strike: Source (It should be near the top )
Step 4: Right Click on Counter-Strike: Source
Step 5: Click Properties
Step 6: Go to the "Local Files" tab This is especially helpful when dealing with base bsps
Step 7: Click Verify Game Files
Step 8: Done! Enjoy cs_italy!