Some can be found close to the Lighthouse area of the beach. With Patch 1.3 I have never seen any outside of a refrigerator. This increase in difficulty and rarity was probably added to make Diamonds harder to acquire. It's probably also why the XP value was increased 10-fold.
In the Laboratory there are three refrigerators that, like the ones in the abandoned houses, may contain a bottle of Champagne. Two are located in the same room as Doctor Robert West and the other is in the section that is unlocked by Bob during the side quest "Rats in the Lab".
Outside the Laboratory, in an inaccessible room. A refrigerator can be looted through the window near a white broken down car.