Water-based Aroma Scent

Last year I bought an air-freshener humidifier for less. It was on sale at a mall with a bottle of aroma oil in green bamboo scent. True to my excitement we were able to consume the oil in a short period of time faster than how it has been suggested without me knowing that the refill of such is not commonly found anywhere. Now I am having a hard time looking for one as the packaging says that only water-based scents are suitable for the revitalizer. There was one available that we’ve seen in a hardware but the cost seems to be to much for the purpose. I wish I can find one online.