kk, I don't have an Ion, but all the guys (basically) that I train with do.
Are you in a paintball club, or play at a site that lets own gunners play regularly? If you answer yes to either of these, they should have HPA. worth a call to check, but basically everywhere thats serious about paintballing probably will have. If you're not in a club, find one and Join! you will find it's far cheaper on paint once you have your own marker and play with a club as they don't have to pay for the day to day maintanance on your marker etc, which sites basically include in the paint price (thats why rental balling cost so much).
Ok, thats out the way.... Find a place that specialises to get your Ion, For example, Jim Frensham at Warped in Wolverhampton. His team Wolf City pretty much all play with Ions and he techs Ions at national events. If ANYONE makes a part for an Ion, he can get it for you. and probably has it in stock anyway. check the warped paintball website and drop him an email. The guy was the first to email me back when I started, and he's played with the best in the world at the highest level. plus, he'll only suggest what you really want, not just sell you stuff cos he can.
His Ion is truely unbelieveably fast, trust me, I've been on the recieving end!
You can't go wrong with an Ion... they're the way forwards!