OS X 10.3.9 Update available?
Google can always find OS X/macOS updates if you use the keywords 'combo update' followed by the main version - e.g. combo update 10.3

The file is at https://support.apple.com/kb/dl496

A combo update can update anything from 10.x.0 right up to itself, without needing individual updaters for the in-between versions.