Hello,
The Widowmaker configuration was the personalized configuration used by Natasha Kerensky when she returned to Clan Wolf. As such, it would be exceedingly rare to encounter. Still, it's an Omni configuration that uses established technologies, and so it can be duplicated by Widowmaker Wannabes (see what i did there?) at will.
Hopefully that helps.
Thank you,
- Herbert Beas
BattleTech
Catalyst Game Labs