At one time we had the setup for electroplating nickel and copper. However, it yielded poor results (IMO) and IDK if we ever resolved the hazardous disposal issue (the biggest issue is the heavy metal effluent). Any plating solution we might have in house is a community resource with all the challenges that accompany that.
On plastic, we used a conductive “paint” as the substrate and as you would expect, it gave a fuzzy finish.
Although the article @Russell_Crow linked looks interesting, 3D printing doesn’t yield a surface finish suitable for plating. The plating is so thin that it isn’t going to fill any voids or surface imperfections. I would be interested to see how the article overcame that issue. Perhaps the “graphite paint” …
You might also investigate electroless plating instead of electrolytic plating.
In commercial use plating on plastic would be done with electroless plating; first layer copper, finish layer nickel. That’s what’s used to make “fake chrome” on plastic salt shakers, etc. Proper chemical cleaning is crucial to surface finish. Nickel can also be plated electrolytically but still requires a base coat of copper.
If you search on talk, you will see various discussions of this topic, including various suggestions for chemicals. IIWM, I’d prefer electroless because it’s just a chemical process without any electricity. I’d also buy all my own chemicals because anything we might have in house is a community resource and I promise you it has been contaminated beyond anything you’d like to see on your parts.