You may or may not find them in a local outdoors store, or a luggage store, and you can definitely find them at
R.E.I., online if you have to, or at
a Container Store. You may possibly find a 3 oz. bottle, which is fine, in the travel-size section of a drugstore or department store. They are becoming easier to find, because these bottles are what you have to put liquids in when you fly on an airplane.