If you aren't lucky enough to have a Miller’s Salvage nearby, here is where the "blue gold" usually hides:

Miller, a man whose skin looked like weathered leather, appeared from behind a stack of tires. "Looking for the blues, are you?" he asked, kicking a 55-gallon drum that rang with a hollow, sturdy thud.

They often buy soap and wax in these barrels and give them away or sell them cheap once empty.