I get mine done at Beer Necessities on Old Alabama Connector in Alpharetta.  Costs $32 for a 10# cylinder.  My experience has been that the paintball locations don't want to fill anything beyond their small 2.5# cylinders and there's no longer an Airgas here that I can find.  There was a place up on Hwy 9 in Cumming that would fill them but I can't remember the name of it.  They were quite a bit further away from me though so I just stuck with where I already go.