Unlock Location:
- To get the
Stray you will need to kill the boss known as Pango Bango, right below the Tendercage on Ripper Drill Site.
Farm Method:
- Defeat Pango Bango who can drop Stray as well as the
Prince Harming and 
Phantom Flame. - Reset Moxxi's Encore to replay.
- Farm until Stray drops.