You can make one easily. Go to store that sells tropical fish, buy a box of activated charcoal, then using a length of tubing, install some hose barbs. BUT, before yoy wast your time and a few bucks, it wont work. I tried it using a Brita water filter cartridge!!

What I ended up doing is adding a stand off about 4-6 inches, installed in the vent hole of the gas tank, then taking a fairly long roll of gas line hose, making a couple of complete circles, then routing outside the car. It's about 90% effective. Any gas that condenses will be sucked back into the gas tank. You also need to use a non-vented gas cap. This was all documented in a thread about 2 years ago here - Gasoline odor