I'd just make your own standard, specifically for a refractometer (as mentioned earlier in this thread Randy H-F has an article about how to do it (
http://reefkeeping.com/issues/2004-06/rhf/index.php). Half decent balances are not that expensive, particularly for larger weights, and table salt is super cheap, as is a gallon of distilled water from the drug store (or if you have an RO/DI system). You can make up a 3.65 weight percent sodium chloride (use standard table salt, not any fancy stuff) solution using 79.3 grams of table salt and 2104 grams of water. If you get a decent scale that works in the 79 gram range you could then just weight the water in small aliquots (portions) and keep adding it to your container.