While "free" downloads are often sought through third-party sites, these files are legally restricted and typically require a valid Cisco service contract to download from the Official Cisco Software Center . Relying on unofficial sources can expose your network to compromised firmware or malware. Post: Cisco IOS Release 15.7(3)M8 for 2900 Series
The 15.7(3)M series is part of the "Extended Maintenance" train. The --FREE-- Download C2900-universalk9-mz.spa.157-3.m8.bin