Do you mean anodizing aluminium or electroplating steel to look like cad plating?
As cad plating is no longer done you will need to have steel
zinc plated and then passivated either with the yellow/gold or an aluminium/silver finish. I just had a whole bunch of stuff PROFESSIONALLY done for $60 which I thought was much better than farting around trying to do it myself.
In hindsight I wish I had gone for the aluminium/silver finish rather than the yellow/gold.