0 to 30psi and 0 to 60psi is ideal, but you can use one up to 0 to 200psi. Past that, they may be worthless for our use.
Look for regulators that have a CGA-320 (for CO2) or CGA-580 (for inert gas, but you can either use an adapter or exchange the stock nut and nipple for a CGA-320 or high purity regulators that have stainless steel diaphragms (these are fine if the gas service pressure isn't too high).
Anwar, that is mentioned in the Victor link, sells Victor high purity, chrome plated, stainless steel diaphragms regulators that have a CGA-320 nut and nipple and also a 1/4" MPT x 1/8" MPT adapter. He is good to work with. Several people have ordered from him.