In the absence of other replies, I have used Prahran Platers in Malvern Rd next to the police station, they have been there for years and I have been dropping bits in since the 80's and haven't had a problem. I have also been to a place on Nepean Hwy next door to Brakes Plus at the intersection of Patterson Rd. He is an old bloke also been there for years. Now I have only had polishing and metal work done there but I can't be sure he does plating. He made my grille look like new when a 4WD put it's tow bar through it. I hope this help as a start. Not sure where you are though.

I had all the plating on my car done by Excellent plating in Moorabbin. Got very good results, however I did send everything to an abrasive blaster to get it clean first, as the acid tanks didn't always work. Turned out to be an expensive process for me, but cheaper than chroming and the results were fantastic.
Also, make sure you get fasteners de-embrittled, or you may as well just buy new ones.

Expensive in that some places charge by weight and theres a minimum weight charge.
Best to ring places for quotes.
I'd be de-embrittling the calipers if I got them plated. Some people will probably say it's not necessary, I just do it anyway.