I’ve had one or two done before. Gold won’t deposit on to any base metal and it was recommended that I got a flash of nickel put on first which is a good “primer” for gold plate. My triggers were steel.
I got it done at a company I used to work for who had an electroplating department. It is possible, just bare in mind it could be a two part process at two different suppliers. It’s unlikely a jewellers will nickel plate.
Cheers
Greg
Edit: something else that crossed my mind, if the trigger is aluminium it could be gold anodised.