Before diving into downloads, we must define "extra quality." A standard post processor outputs generic G-code. An extra quality post processor does far more:

Standard free downloads rarely offer these features. Most are generic, untested, and potentially dangerous.

Surprisingly, some developers host open-source GibbsCAM post configurations. Search for gibbscam-post-processor on GitHub. While rare, these are often "extra quality" because they are peer-reviewed by engineers.

Communities like CNCZone, Practical Machinist, and Reddit’s r/CNC sometimes share posts. Search for "GibbsCAM Fanuc OM post" or "GibbsCAM Haas VF post." Users often modify stock posts and share them.