I get it from excellent-supply.com only because they've always given me great customer service and nobody local sells it. For some reason I don't save any money having it shipped here from Seattle (90 miles away) versus Florida (3000 miles away), go figure.
For my first order I got the 16 oz. bottle and a 1 gallon. I re-fill the smaller bottle whenever it runs low, it's the kind where you squeeze the bottle and it fills up a little 1 oz. area at the top, then you can just pour out 1 oz if you like. Easy to use, small package, and fits in my spotter bag.