I live in Delaware, OH. I found a couple places nearby for CO2:
Barley Hopsters in Delaware
ABCO Fire in Dublin on 161
Geer Gas in Columbus just off 315&Goodale
Barley Hopster is a local Homebrew supply store. They have co2, but they underfilled my tank. They do not have the proper equipment for and complete a proper fill. They are extremely friendly and a great place for your home brew needs. Just maybe not for CO2...
ABCO Fire supplies CO2 for fire extinguishers etc. They also will fill a co2 tank for you. I have not tried them yet, but understand that most of these places that fill for fire extinguishers etc have the proper equipment and fill tanks properly.
Geer Gas is awesome! If you have the option, go there! These folks KNOW what they are doing and are very friendly. They also will fill your tank while you wait, which only takes a few minutes. They have very good prices and charge about 12 bucks for 5lbs of co2. You don't have to worry with them, they always make sure you get ALL your co2 per fill. I had one minor issue with one of my tanks, they not only replaced it for free, but upgraded it to an aluminum tank! They also threw in a free fill! Like I said, these guys are very friendly, very knowledgeable, and are the place to go for your co2!