Buster wants to send his 1911 away to have it made very shiny , like a mirror.

I suggested white grips or very close to white grips would look great , but he wants the grips to match the finish on the gun.

what would the grips have to be made of for them to be plated ?

Metal. I think these can be plated, most likely. They offer them in shiny “gold” for less than $60.

http://www.adamsandadamsengraving.com/photog01.html

Aluminum is a common options for metal 1911 grips. Aluminum could be plated, but anodizing is a more common surface treatment, and it can likely be anodized to a shade complementary to whatever steel finish he ends up choosing.