I know this is an old thread, but I have been looking for the same info everywhere and found out Koetter Fire Protection service in dallas does refill CO2 tanks. For a 10 lb tank, they charged me 20 + tax.. If I remember correctly the guy who filled said, they charge a minimum of 20 $ minimum regardless of the tank size. So a 5lb or a 15 lb is going to cost the same. I took my tank and they filled it right there and I was out in 10-15 min.