Try looking for Varathane and similar products anywhere that sells wood stains and sealants. Look in smaller hardware stores as well as the larger places. Varathane is also available on-line. These products usually come in gallon- and quart-size cans, but they are sometimes available in as small as a ½-pint can. A little goes a long way. To extend shelf-life and prevent contamination of your whole supply, don't work from the can. Instead, transfer a small amount of the finish to an "easy access" container and make sure that the can is tightly sealed and properly stored. Some suggest that store Varathane away from light, such as in a black film canister.