Here you will find the latest download links from the afterSource project:

de_dust_aftersource                      de_dust2_aftersource

de_port_aftersource                      de_aztec_aftersource

de_cobble_aftersource

You can also download it at ModDB project afterSource 

Download the files and extract to your cstrike\maps folder.

Example: I:\Steam\SteamApps\youraccountname\counter-strike source\cstrike\maps