As far as I know, at this time, Ruger will not perform ANY maintenance on the Six series DA revolvers because of them being out of production for so long. They basically do not have any parts for them anymore also.
Best bet is to find a gunsmith who can do a good reblue it for you. Be advised, a reblue will not look like it came from the factory due to the changes in the chemicals used to blue guns nowadays.
The other option, depending on how you are going to use it, is to just leave it as is and shoot it and keep it cleaned and lubed or have someone Cerakote it for you. With the Cerakote you can have it just about any color you want, or multiple colors (frame one color, cylinder, hammer, trigger, etc. a different contrasting color).