APMEX Inc. based in Oklahoma City. Oklahoma is the worlds largest online retailer of precious metals APMEX offers gold silver platinum and palladium including coins bars jewelry IRA eligible products collectible coins and commemorative items.APMEX Inc. based in Oklahoma City. Oklahoma is the worlds largest online retailer of precious metals APMEX offers gold silver platinum and palladium including coins bars jewelry IRA eligible products collectible coins and commemorative items.