Sorry I lost this one.
You asked about small slip stones. They don't seem to be that easy to come by other than some specialty sources like Brownells or KBC or Enco. But there are a couple of options. One is small diamond files in the fine grade. Another is the Lansky sharpening stones on the holders used for knife sharpening. The stones can be used while on the holders or in the case of the triangle shaped white ceramic stone I was able to carefully snap the stone off the plastic holder. But instead of that on the next one if the plastic gets in the way I'll just trim off the plastic instead since it was on there pretty hard.
Wholesale Sports handles the Lansky line. And I'm sure you can find them at other places as well.
For deburring and polishing you really want the medium to fine end of things. And in fact you'll only use the medium for fairly heavy deburring. Most of the work is going to use the fine and extra fine stones.
And when you get right down to it for casual deburring which isn't shape critical some silicon dioxide "WetorDry" sand paper wrapped around a hard block can work just fine as well. 340 and 400 grit is a good size for general deburring of this sort. The paper wears out fairly fast when used for this sort of work but even with frequent replacement a sheet of the stuff cut up and used in the small amounts needed will easily do two rifles from one sheet of paper.
In particular pay attention to smoothing out the ejector. Out of the 4 Rossi rifles I've done now this one part gained me the most when it was deburred. The last two had seen some hand work at the factory and the ejector was part of this work. So I found that on the last two from about two years ago that it was primarily just a case of checking things out, admiring the hand work on the ejector, guide rails and carrier detent notches and installing the new spring kit from Rusty.
In these last two instead of the new sight to replace the lock I just put in buttons cut from the soft tang end of a 9/32 drill. The little 1/4 inch long piece left the drill bit still usable. The end was lightly domed for appearance and a notch to accept the locking pin filed in using a small round "jeweler's" file. The plug was then cold blued and installed. I used the old safety as the model to work from. The new plug is simply shorter and doesn't intrude down into the firing pin area. The little spring and ball were removed at the same time. As metal working projects go pretty well anyone with a drill set, hacksaw, hand drill and some files should be able to make something of the same sort.
The rifles in question are all being used for cowboy action. And in this case receiver mounted sights are specifically against the rules. Otherwise I'd probably have made the plugs as sights as well.