I think you may have trouble getting many takers on this because a "good" stonewashed finish is more than just tumbling.
(I'll take your money and just tumble your parts in my SWECOs for however long you specify, but you probably won't be happy.)
The finish on the parts has to be really good BEFORE you do the stonewash, otherwise it will just make all the imperfections jump out and there'll be a lot of back and forth on each part chasing down little imperfections as you try to "stonewash" them.
Someone might say, "... but you can tumble parts a long time and take out surface imperfections."
That is true, but by the time you get those little scratches out of the flats of your blades, you will have badly rounded off every edge on your part.
IMO, a "good stonewashed finish" is one where you have the industrial stonewashed/tumbled look without loosing too much definition on edges/contours. In fact, the edges should still be crisp and distinct.
That means finishing the parts to a fine hand-rubbed finish first, with emphasis on trying to find any imperfections (not hide them in the 'scratch lines"), etc. Then running them in the tumbler, preferably with a lot of weight in media, for a relatively short time.
The way I do it, it's one of the more time-consuming finish options, ironically, and all that time is invested BEFORE the parts get near the dancing rocks.