Stratix III FPGA development kit

Have you tried restarting the computer? I have seen a case where the device family appeared after a system restart, although this may or may not resolve your issue.
 

I believe you are installing using the individual device files (.qdz) instead of the complete installation package (.tar), correct? For legacy Quartus versions, using the complete installation package is generally more reliable.
 

If the Stratix III device still does not appear, you may consider performing a clean reinstall:
- Uninstall Quartus completely
- Ensure there are no residual files left in the installation directory
- Reinstall Quartus using administrative privileges
- Verify that the installation package (.tar) is not corrupted (for example, by checking its checksum)

After installation, create a new project and check whether Stratix III appears in the device selection list. 
If not, try restarting the system again and confirm if the issue persists.

Regards,
Richard Tan