I agree with Bailey on this. Go to the pet store, and get "Activated Carbon" it will be in the fish section, and used for their filtration systems. I have yet yo refill a filter, but have made one, and it is the EXACT same thing in our scrubbers. (your water filters too if you have one) This is the exact product I used.
I have not personally bought a carbon sleeve, but think I will now. Thats a great Idea
@Bailey Can you recommend a decent sleeve for that bud?
With the cfm or M3/hr you want them to match as close as you can. The air can either pass to fast, or slow and give you undesirable results. Ultimately though, trust your nose, or in my case I trust my non-smoking wife's nose. There is a chance the carbon in the filter was no good to start. Some things will kill a filter fast, like being stored in open air, high levels of humidity, the higher the levels, the worse the filter will preform. If you do go and refill the filter yourself, be sure to tightly seal up any left over carbon for later uses. Carbon is also used in the same manner as silica, and rice are for drawing in moisture, and regulating rH in things like humidors, seed containers, pill containers, and so on.
If you decide to purchase a filter still, I'd be happy to help you find one, and if you need help refilling the old one, still here for a hand. Take care and if you need just hit me up.