I had to run the co2 through a couple of regulators before it was down to carbing pressures, since it's coming out of the tank at 850-1200 PSI depending on temperature, you'd need a high pressure one to turn it down to under 400 PSI and a low pressure on to get it under 100 PSI reliably. Try finding a 2000-2003 high end model marker (autococker, older impulse, shoebox shocker, wrath, rainmaker, etc. No angels or intimidators those run on HPA only), most will have both and can be had for under $150. I made mine with autococker parts, I get about 5 corny fills to 20 PSI with a 12 oz tank.
My carbing setup:
12oz CO2 tank, hooked up to WGP ON/OFF ASA, wooked up with braided steel line to a system x high pressure regulator (output set at 300 PSI), hooked up to a palmer's persuit ASA to 1/8 NPT adapter, hooked up to a brass T with 1/8 NPT holes (one plugged, one inlet) one of which has a standard 2004 WGP bullet Low Pressure Regulator for autococker type markers (set at 10 PSI), hooked up by 1/16 ID urethane hose to a 10-32 barb on a 10-32 to 1/8 NPT adapter on another brass T, on the holes: inlet, 0-160 PSI gauge, outlet to reinforced vynil hose hooked up to the ball lock fitting that goes on the corny keg.
this is what it looks like:
http://img504.imageshack.us/img504/5964/carbrig.jpg