Jim,
If it is just some light spotting (metal discoloration) you might try some Hoppe's #9 and some VERY fine steel wool.
If the staining is persistant you might try some very fine crocus cloth, available in the sandpaper section of most hardware stores. Practice with it a bit on an old knife blade or something similar so that you can see the effect it has before taking it to your gun.
Another product that might help, if the spotting is not too bad, is NeverDull. It is a metal polishing product sold by most automotive stores. Basically, it is a can of cotton wadding that has been permiated with a polishing compound. Works great on chrome, nickel, copper, brass, etc.. I would imagine that it would work on polished steel as well.