I find them all over the place - in abandonded homes, random containers, shelves, and so on - but they're far from my primary source of income. Repairing weapons and selling those (especially with the Jury Rigging perk) makes money several orders of magnitude faster.
From the unofficial wiki:
Locations in New Vegas
Brewer's Beer Bootlegging - 1 can be found in the cellar, in an average locked explosives crate.
Lucky Jim Mine - 3 bottles can be found just left on the shelf after you entered the shack.
Cerulean Robotics - 1 can be found in the second room near the doors in between 2 metal box
And as I said before, they're pretty much everywhere else between other clutter.