I play paintball personally, you can get adaptors for a scuba tank to fill some HPA tanks . Co2 is alot harder on the guns and if your looking to get more out of your guns then youll want HPA so that they dont brake down. Large Scuba fill tanks shouldnt be to hard to find at a fair price.
Adam's right. CO2 is nothing but trouble for Paintball Markers. They can cause velocity drops when shooting strings of paint, can cause freezing, or even chop balls, and EVERYONE should know, chopping is the LAST thing you want while playing paintball, EVEN MORE SO when you're running a zombie shoot!
Glad you got something figured out. Good luck.