I know of no source for "aftermarket" cylinders for the Blackhawks. Of course a number of the gunsmiths that specialize in conversions of Ruger single actions, like Hamilton Bowen, could make a custom nonfluted cylinder, but I think the cost would be rather prohibitive for a merely cosmetic change.
As to the stainless finishes...Ruger has used a few different looks on their ss firearms. The stainless Blackhawks do have a brushed finish, as does the Single Six, GP100, and others. Many of the New Vaqueros come with a polished finish to resemble nickle, as did the fixed sighted Old Armys before they were discontinued. Then there's the odd grey finish used on some of the Super Redhawks and stainless rifles. I don't believe any 45 Colt Blackhawks have worn any finish besides brushed, but there's always the possibility a small run in one of the other styles was done for a particular distributor.
The finish used on this Ruger (http://www.gunbroker.com/Auction/Vie...Item=151700576) is Mag-na-port's "Velvet Hone", a proprietary and attractive bead blast finish they use on their custom revolver packages. This was never available from Ruger on a production gun.