Yes, there is something you can do. Birchwood Casey sells a couple of different gun bluing products. One is a liquid that comes in a small plastic bottle, the other actually comes in a small marking pen, just like a felt tipped Sharpie. Neither of these products is what you'd want as a first choice, as they will not last as long as a factory bluing process, but they are very inexpensive, very easy to use, and can do a fine job touching up small dings and scratches. They are definitely worth a try. I've not used the felt pen version, but I have used the liquid that comes in a bottle. The key to getting decent results is to make sure that the surface you wish to touch up has been de-greased completely, otherwise the bluing rubs right off.
If you can't find them at your local store, you can order a felt pen version from Midway USA. They also list many other products that are worth looking into. Good luck.
Here's a link:
http://www.midwayusa.com/rewriteaproduct/178848
scratched barrel
