where to get activated carbon?

So I've had my carbon filter ..an 8 inch filter, for a year now and I'm starting to notice that it doesn't quite cover all of the smell now. There is a light pot smell in the house now.

Should I buy a new filter or should I buy some carbon and put it into the filter?
Aslo, how long should these filters last? I feel like for 150 bucks it should have lasted longer than a year?

Ive got like 5 years one one. They can be cleaned, and also buy another one and use both. Its still working even if not perfectly.

I'm thinking now that my fan is too powerful. I had it turned low but have had heat issues in my tent lately so I turned it full. Ever since I've been smelling a hint of skunk.

8" fan is pretty big, how big is your area?

3x3 tent. 8 inch filter,

Way too big a fan for that size space. A 4" fan will work great on that size and the filters are 60-80 bucks each.