I just want to add some additional information to the solution of Felix Pie.
When you find yourself in the bar in the rail nomads camp,it is actually sufficient if you just buy one bottle at the bar. Just have it in your inventory and wait for a red text saying "stolen by Scotchmo". After that you can just enter his inventory and transfer the bottle back to another inventory. He will simply steal the bottle again.
Rinse and repeat and the achievement will unlock.
If you need more help finding the stash , refer to the video below by RPG Division
Hope this helps!
Any improvements? Please let me know in the comments below!