If you're looking for a specific save file, you can download it from various online sources. However, be cautious when downloading save files from untrusted sources, as they may contain malware or corrupted data.
Availability and Analysis of Per-Mission Save Files for Far Cry 3 on PC Platform: PC (Windows) Game Version: Standard / Blood Dragon (Structure applies to both, though files are not interchangeable)
If you don't want to download someone else's save but want to create your own mission-by-mission archive, one tool stands out above the rest.