Airgas will swap out CO2 cylinders locally but won't typically refill your own tank.
Your best bet is to find a welding shop that will refill your tank. There aren't that many that I've had good luck with in Louisville. Typically have to travel into Southern Indiana for the best deal without crazy hassles.
after calling a few places, the best place was a welding supply shop called Modern Supply in elizabethtown. only cost $12.39 to change out a 10 lb co2 tank. they can refill but they send it out and you get it back in about a week. i was able to swap my aluminum tank for another aluminum. if you're around fort knox, the price is reasonable and closer than louisville.