Answers

I'm not familiar with cartridges but you can buy an aromatherapy canister (hot tub warehouse online has them) in which you put aromatherapy beads whichare available many places (such as spa depot). You can add aromatherapy beads and liquid directly into the spa as well.

There is several different places you can purchase these. Walmart has some option, home depot, bed bath & beyong, etc. Maybe check these places online and see what they have. It would probably be very simple for you to find the best product online, otherwise try calling one of those store to ask if they have any in stock!