Its a bit out of my field, but perhaps electropolishing? The process might present a bunch of other issues but I understand its one used commonly in manufacture of stainless cookware, etc. Check with an electroplating service to see if they can electropolish for you, and for goodness sake consider metalurgical issues on the alloy you'll be using if the size of the piece and cost are not prohibitive.
I've found stainless very difficult to polish by[expedient] mechanical means
Regards
d
Companies like 3M produce a host of mechanical polishing products for S/Steel. It is however a specialist field, and for exacting applications I would send it to the specialist S/Steel finishing shops.
Try their website: www.3m.com and place "polishing steel" into the search box. You will find a lot of possibilities.
Regards
Niekie Jooste