You should be able to do a google search on the product and find it on Amazon or ebay. Here is one example (offsite) - https://www.amazon.com/dp/B07V2T7Y35/?tag=reefsanc-20 Double check thouigh since there may be different sizes.
Although this kind of begs the question, what kind of aquarium system are you running this on? This is because filters that use such cartridges are usually not the filter of choice for SW reef systems.
