Carbon filter question

I would like to build my own filter but have not been able to find any carbon yet.
Generally my question is, is there a wrong kind of carbon i can get? If i find some at a pet store that might be for an aquarium then will this not work for air? What other places can i look, i went to a hardware store today and they didnt have any. So besides a pet store what other places have this?
The local head shop only sold complete carbon filters but not just the carbon.

check your local pet store in the fish section

yeah thats what i thought, but is that the right kind?

yo, my dad works at an HVAC place and they have big carbon filters that you could cut down to whatever size you need, so think more towards air conditioning.

I remember reading some were that it is active carbon that you need. I will be making one in a wk or so.