Don't do what I did... Got my setup all set... ready to rack into the kegs... then remembered that I needed to get my CO2 tank filled
I couldn't find any local places that would fill my CO2 tank... they all wanted to swap it. But I went out and bought a nice alum tank and I wanted that one since it's nice and clean...
In the end I went to my LHBS and they were able to get it filled... Took them 10 days

but they warned me it takes a while..