You may possibly find a 3 oz. bottle, which is fine, in the travel
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.
If you can’t find one anywhere, then you can just use any plastic bottle with a spout that squirts, like a Rubbermaid picnic bottle or a kitchen squeeze bottle.
The best, once again, is a small travel squeeze bottle, which is listed as a 4 oz.