agree with Mete
I wouldn't normally go after a chamber with scratches in it unless it is causing problems with extraction or causing some other problem. If it isn't bothering the operation of the gun and messing up the brass and you reload for the gun, I wouldn't worry about it and keep on shooting it.
Spring stock is spring wire that is straight. You an buy it through most metal supply stores, machinist supply stores, and places like Brownells. I get the variety pack that has different sizes in it and will use a flexible one when I need to work in a semi-auto. I use it the same way which is chuck it up in my Foredom tool and then tape sandpaper to the end of the stock and then roll it up a few wraps around the stock by turning on the Foredom tool and let it wind the paper up for me.
Once it is wrapped around the stock, I cut off enough so it will fit the chamber very loosely and apply some spray lube like WD40. I let the flap of paper spin around and this is what polishes the chamber for me. You can use a flexible piece and let the stock bend enough to go into the chamber and still use the foredom tool to move it back and forth to polish without any problems.
Normally, scratches shouldn't affect you too much and like Mete said, I wouldn't worry about them unless you are having extraction problems or are shooting heavy reloads. Normal military rounds shouldn't be bothered too much by the scratches. If they are causing problems, you might have to remove more materail than what you would be able to remove and would need to have the barrel replaced rather than polishing out some deep scratches. Best of luck with it.
I wouldn't use a bore mop simply because the surface will give too much for you and not provide a very good surface when you are done polishing with it.
