Once you've satisfied that your accuracy problems are caused by throat erosion and not simply by copper fouling, you might try some David Tubb Final Finish bullets. These are abrasive bullets that you need to handload; they can often extend the useful life of a barrel whose throat is eroded a bit. I have used them in brand new barrels and they definitely helped with accuracy.
Here's a link that describes them...
http://www.jarheadtop.com/article_finalfinish.html
You can buy these bullets in various calibers from Midway, or from the site above in .308 and .223 caliber only. Again, these are bullets ONLY, not loaded ammo.