If you had nickel, stick with nickel.
I replate electric guitar parts in nickel all the time. You can do it yourself. Check out Caswells, plating supplies, and go with actual electroplating. Nothing quite looks like nickel plate. Chromium platings are too rich, deep and mirror like. Nickel is silvery and brighter. Cast parts are notoriously the hardest to plate, and extruded parts like pipe & wire are the easiest. Copper pipe is what every DIY plater starts with. Any good plating job with nickel, gold, or black oxide needs a copper or brass underplate, so you plate the gun in copper or brass, then plate it in nickel, after the copper plate. This type of nickel plating will NOT flake off, bubble off, or pit. Like painting 98% of the job is in the preparation work, such as stripping the old plating, polishing, cleaning, electro-cleaning, rinsing, pre-etching, rinsing, then you do your under plate work, and the same cleaning steps, (without the stripping) all over again. You use a 12 volt power supply, electro-cleaning, electro-pre-etching, and a nickel plating solution with a nickel anode, and plate up your gun parts. The parts I do are smaller than a gun frame, but I do a lot of cast parts. My beakers will not do a gun, but I assure you a good experienced plater will make it look absolutely gorgeous. I am an amateur DIY'er and I do very nice plating, but only on parts no larger than 4 pocket combs, stacked together.