Polishing a Micro Seiki RT 3000G Gunmetal platter

Give it to a Metal Polisher and then aVustom  Automotive Sprayer to Multicoat Laquer Finish. These treatments are not expensive as a Polisher will see this as a Pin Money for cash job and the Sprayer will coat it when the Pot has Laquer in it. 

Lets rephrase the OP's inquiry.

I have recently received a Imported from Japan Micro Sieki BL 111 Turntable.

I am keen to keep it aesthetically appealing, as this Model has a used market value of between $4K - $6K.

I have a Platter which is in need of being returned to a Highly Polished Finish.

Can a method to achieve this be recommended? 

??? I have not revealed my experiences or competency levels to achieve this as a  finish by myself as the option.

No Lacquer applied will keep the metal exposed to oxidation and dulling will occur.

Usually non ferrous metal will be welcome to oxidise and gain a patina, it is attractive on furniture.

I have a Tenuto Platter Mat, and I know these are with a Lacquer finish.

Lacquer is an application carried out regularly by Custom Spray Paint Services, hence my earlier suggestion to use such a service once a Professional Polisher  had Bright Polished the Platter.

I am not anti DIY Polishing, I have in the past taken Platter Rims to a Bright Polished Finish.

In this case the Value of the BL 111 TT on the used Market suggests it will be aesthetically attractive if dealt with by a Professional Service.