you could buy or rent the canister, you want to find a place near you that fills it.
probably try welding shop or perhaps a paintball place. i know walmart fills the little paint ball one, not sure if they do bigger ones.
next you need 3 things
airline hose, you can use regular hose but it cracks after a while(months), silicon is what you want to get i think.
a c02 diffuser and a bubble counter, search ebay. ADA prices are out rageous.
the kit from drsfosterandsmith is what I currently have, and i got my co2 tank from a local beverage company. previously when I lived in Hawaii i ordered my co2 tank from here: http://www.co2-canisters.com/ Much lighter when they're made out of aluminum, but here I wanted to be able to get the cannister tested every 5 years and I wasn't sure if the local shop would do it on ones not from them...