Look for the c2800nm-adventerprisek9-mz.124-15.T1.bin (or a similar stable release for the 2800 series).
Always verify the integrity of your download using the MD5 checksum provided on the Cisco download page to ensure the file is not corrupted. Step-by-Step GNS3 Integration Guide cisco 2811 ios image gns3 download for 19
In the screen, you can add interface modules. Slot 0 contains the default FastEthernet ports. Look for the c2800nm-adventerprisek9-mz
Click , select your image, and follow the wizard to set the platform and chassis. select your image