I just found this site while tinkering around on the net... This site carries 50+ pound empty cylinders made for CO2. The smallest one they have is a 2 pounder which would be good for the small setups. Anyway... this site seems to have all the info about the tanks and where to get them filled SO WHAT ARE YOU WAITING FOR!!! GO CHECK IT OUT!!!
http://ceisites.com/carbon.htm
let me know what comes of it.